Dear Steve,
As promised, I give you an answer (just) before the Christmas break:
1) No real showstoppers were identified. However, many issues remain to be studied in detail. The Crab Cavity will be used in KEKB until June 2010 (at the earliest) or end of the year 2010 (at the latest). Knowing that it will then have to be removed from the tunnel, modified (by the KEKB people) to have the frequency of 511 MHz (instead of 509 MHz) and a high Qext (changing the coupler), we estimate that the crab cavity could only be used/tested in the SPS in 2012.
2) The best location for the KEKB Crab Cavity seems to be the location of COLDEX.41737, which is not used anymore and which can be removed. The 2 main reasons are the space (a cavern is required as the Crab Cavity is too big to be in the tunnel without perturbing the transport) and the available cryogenics required for the superconducting Crab Cavity.
3) As collimation could also be an issue with Crab Cavities and as a 2nd collimator (from SLAC) should be installed in the SPS (in 2010 or 2011), the best location for the SLAC collimator was studied and a request from the CCinS working group was made on 17/12/09 to the relevant people (http://emetral.web.cern.ch/emetral/CCinS/5thMeeting_16-12-09/PositionOfTheCrabCavityAndTheSPScollimators_2.pdf). Note that the Crab Cavity is horizontal and the 2 collimators are also horizontal, which is ideal. With the proposition, the phase advances are such that almost no crab effect is seen at the 1st (SLAC) collimator, whereas the full crab effect is seen at the second (CERN) collimator. However, to do so the vertical Ionization Profile Monitor needs to be moved before the QD.517 (the relevant people are already informed).
4) A first time estimate to remove COLDEX is ~ 2-3 weeks.
5) A first cost estimate to change the PLC and for the supervision of the old cryogenics system (TCF20) is ~ 200 kCHF.
6) Concerning the required IOT(s) for the RF power, Eric Montesinos could order the 1 or 2 which we would need (1 might be enough if Qext is high enough) together with the IOTs he will order to replace the SPS klystrons (the cost of 1 is ~ 400 kCHF). We will have to tell him asap. A pending issue is the space needed for them.
7) As the Crab Cavity will come from Japan after a long trip and some modifications, it would be wise first to test it somewhere at CERN (SM18?) before installing it in the SPS. The cryogenics should be already there (at SM18) but an RF amplifier would be needed (may be the same as the one we will use in the SPS). However, it could be that there is no much space there (I don't know, to be checked).
8) To take a final decision (on the usefulness of the SPS measurements with the KEKB Crab Cavity), MDs are proposed in the SPS in 2010. One of the most important measurements is the effect of the RF noise on the horizontal emittance. To study this, one needs first to have a beam with good "horizontal emittance lifetime" (and not only the usual beam current lifetime). Furthermore, the tilt from the Crab Cavity should be at least of the order of the horizontal beam size to see something (which would ideally mean to use bunches with a horizontal rms. norm. emittance of ~ 2 microm and a beam momentum of 55 GeV/c). Therefore, it is proposed to perform some MDs in 2010 in the SPS to study the horizontal emittance lifetime in coast (at 55 or 120 GeV/c), without a Crab Cavity, with few bunches (first, and then few batches to challenge the RF, introducing transients) spaced  by 4 × 25 = 100 ns (to be more precise 4 × 24.95 = 99.8 ns which is compatible with a frequency of the Crab Cavity of 511 MHz). The good news is that the 100 ns bunch spacing beam will be prepared next year to satisfy a new request from ALICE. It's worth mentioning that with the Crab Cavity the RF noise could also be studied by increasing (voluntarily) the RF noise and measuring the evolution of the horizontal beam size to define some limit.
9) Concerning the Machine Protection and reliability issues, it was agreed that the SPS should mainly be used to make observations: no SPS interlocks are foreseen at the moment. In principle, there could be in fact 2 kinds of interlocks: slow (on BPMs) and fast (on RF). One might have in 2011 a BPM interlock post-mortem, i.e. the last 1000 turns, to study what happened in case of problem, but the resolution is not so good. Ideally, we would need to put a fast RF interlock. What could be studied is the effect of the Qext to see if the phase cannot go rapidly wrong etc. However, it seems that we will not be able to play with the Qext as it is fixed for KEK. A new design would be required to have different Qext. Reminder: Operationally one prefers to have a low Qext, as in this case we are less sensitive to perturbations. But, from the Machine Protection point of view, one prefers to have a high Qext, as in case of problem the Crab Cavity reacts more slowly. In this case we can live with less power but we are more sensitive to vibrations (phase changes etc.) and offset => Huge transverse impedance! For the measurements, the idea would be to increase the Crab Cavity voltage and study the scaling of the trip rates with the RF voltage. We could also scan the synchronous phase, and the horizontal beam offset, and observe the effects on the beam to define limits of synchronous phase shift and horizontal beam offset.
10) Concerning the SPS availability (as the SPS will have to deliver high-intensity beams to LHC and CNGS), we propose to use a bypass (i.e. 2 beam pipes linked by Y-chambers, one with the Crab Cavity and one with nothing) as was done in the past with COLDEX: for physics, the beams will not go through the Crab Cavity. The Crab Cavity will be moved into the beam only during MDs. Some issues remain to be studied in detail, as for instance the design of a system of rails with motorization etc. (within a height of ~ 20 cm) to move the Crab Cavity (~ 5 tons, compared to ~ 0.5 ton for COLDEX).

I think these are the main outcomes of the small CCinS working group. I could send you more info/details if needed at the beginning of January.
Meanwhile, I wish you a Merry Christmas and a Happy New Year.
Kind regards, Elias.
PS: The web link for the CCinS workinh group is: http://emetral.web.cern.ch/emetral/CCinS/CCinS.htm.