There is a Angstrom (Embedded Linux) variant in the SDE firmware to download from Archos breaking Archos warranty (but not the defects liability by law being two years in europe). My guess is that the seller cannot find out if the warranty was void but only Archos itself (after you put back the original firmware on the device).
Honeycomb has no limitation whatsoever I read at different places. Last year there were many rumours concerning hardware limitations. They did not even post some recommended hardware. The only thing I read is that applications for larger screen sizes are encouraged to be developed. IMO best would be to offer support for two screen types, low and high resolution.