The thing we care most about in interviews (at least of things one can change) is how engaged the founders are with users. How do they know people actually want what they're building? Have they talked to real, live users? What have they learned from them?
We don't care super much how big the initial market is, so long as the startup is making something that (a) some subset of people want a lot, and (b) if that market is not itself huge, there is an easy path into bigger neighboring ones. Basically, we're looking for startups building Altair Basic.