On the FL, I assert that you can get used to anything, eventually, with enough practice and effort. But the consideration is always the ROI on learning to intonate on it, especially if it's unlined and the more exotic it is. Some players are good enough to switch between, for example, 34" and 35" scale unlined basses pretty automatically with a reasonable amount of effort. Others can play 6 string unlined well enough, even above the 12th "fret" that it's worth the investment in time and effort to learn that too (I wasn't one of them

).
My suggestion would be an unlined multiscale would be a pretty large investment in practice to get to where you can intonate it well enough to really feel free to do what you want on it, including gigging with it etc. So I'd recommend, if possible, try before buying, to get at least a broad picture of what you'd be up against. Either that, or just be prepared to woodshed for an extended period of time with it and maybe not be afraid to eventually admit defeat if you have to, and put it back on the stand or sell it, etc.
I've never really been charged up about multiscales even with frets, so for me a fretless one wouldn't make any sense at all. But that doesn't mean I wouldn't necessarily discourage someone else from doing it. I think there are players who already do, so, it's worth a shot.
The only other thing is intonating lower notes gets progressively harder as you go lower. A B string is about as low as most people can go and still intonate it as good or better than a fret can. So going lower than that, fretless starts to become impractical, plus or minus how good your hearing and sense of intonation is... So just something to keep in mind, just as a pure practical matter, if you plan to go lower than the low B....
L