In the case of Blazblue…I can’t speak for the community, but here’s what I think will end up happening.
Given the relatively small size of the BBCS community, people will probably grit their teeth and allow non-Unlimited DLC characters (read: Makoto, possibly Mu) to be legal unless they prove to be horribly, horribly broken anyway (a very, VERY remote possibility now that drastic balance patches are standard policy).
It will be annoying to arrange for every tournament console to have the appropriate characters available, but it’s a minor inconvenience at best. People who care that much about BB will in all likelihood value the diversity added by tourney-legal DLC characters enough to put up with the organizational hassle. (Especially in a small-cast game like BB with characters that play so vastly differently…even two additional characters might present an “in” to somebody who hasn’t really found their niche in BB.) Just keep like a list of people who have the DLC (really anybody who actually LIKES BB is probably gonna take the plunge on at least Makoto) and things will be fine.
Or tournament organizers can keep like a supply of memory units with the DLC on there if for some reason BYOC will be deficient in the DLC department. It’s not like the prohibiting factor is the expense (unless you’re an even bigger cheapskate than me), merely making sure the stuff is on hand to play. With the new console-centric focus of the fighting game scene, this is pretty much the way it has to be.