The Futari BL port isn't even that good, although it's a lot better than playing the game in MAME (emulation in MAME is horrible, the slowdown isn't close to accurate no matter what blitter rate you use or whatever). However, there is a widespread perception that the Futari BL port is extremely good, because it was made by M2. And there is a widespread perception that the SDOJ port is not very good (actually, other than the few extra frames of input lag, it's not far off from the slowdown accuracy of the Futari BL port). It's funny how perception can influence PCB pricing.
Putting SDOJ in MAME won't make a difference on the PCB price, because no serious player will play it that way (due to lack of slowdown or messed up/super inaccurate slowdown). Look at the PCB prices for Akai Katana, DSMBL or DFK BL (all available in MAME, and all run like garbage in it), for example. Pretty pricey. The X360 ports of these games are so much better than playing emulated ROMs, and the same will be true of SDOJ if/when it gets dumped and added to MAME. So people who want to play these games but don't want to pay the high PCB prices should buy an X360 and the ports (they're not very expensive!). If people could find a way to emulate the SH3 games as well as, say, Ketsui or DOJ BL are emulated, then I think PCB prices might come down a bit.
No SH3 conversions out there AFAIK because they're too hard to do to make it worthwhile for the bootleggers out there. CAVE did a great job designing their SH3 hardware to be safe from copying/conversions.
