The only guarantee, hardware-wise, is to disable the mod chip, power off, power on.
I think packet filtering will be enough anyway.
I'm actually a bit surprised nobody has patched the Live! Executables to solve the issue anyway.
There are a number of attacks that could allow the use of a modified machine during an XBL session; that M$ might change tactics in the future shouldn't come into play, because we are talking here and now.
I'm just concerned about the big announcement with NO SALE DATE. I realize the EB2k raid probably killed any momentum on production and sales, but Team Xodus didn't even announce specs until now, 6 days after this 1MB add on was supposed to SHIP (Jan 25th). The timing is suspect, coming on the eve of Pros being shipped out.
If they were on track for a Jan 25th release, these specs could have been revealed well before the raid took place.
Basically, I'm willing to cut them some slack, but I'll be a bit wary until hardware is actually released, or we at least see some photos of the device. (remember, we saw X2 prototypes LONG before actual release)