Are the ROMs shipped with classic Amigas flashable? As far as I know they are not. In other words, if you need a new Kickstart you have to buy new hardware. If you want to use a larger kickstart you buy a Kickstart replacement chip/board that can handle it.
The main issue with the size of the AROS ROM is with the size of Wanderer. There has been talk of creating a Wanderer Lite to get around this issue. Other than that, there are no major components (AFAIK) that will need reworking to make an AROS ROM of a similar size to a classic AmigaOS ROM. For some software, you don't even need a Workbench replacement like Wanderer anyway (such as most games), so for this software the issue of size is not applicable.
Jason already started on "wanderer lite" he called it workbook iirc. =]
