I've basically already stopped crowdfunding things. There's enough games to make me broke anyway.
But this development doesn't exactly make me keen on jumping back in.
Fig differs from Kickstarter in that some backers are investors, who might be happy about getting a return, and some might be ok with screwing over other people because Epic's moneybag adds to the game's budget, but all backers would certainly be in their right to express dissatisfaction.
Mobius' statement in the OP reads like what's uncertain is the platforms beyond Steam the game might become available on. It just incidentally can also be retroactively read differently in today's context. EGS didn't exist in 2015, so it makes no sense why anyone would've expected the PC platform to be what's susceptible to change. This is definitely going back on their promise.
I would demand a refund.
Trust is why I'd opt to crowdfund anything. Break that trust like this and I'm done, I don't care if they're Yu Suzuki or if they managed to cover their asses with vague language or not.
For the record, the Shenmue 3 page does not mention "steam", but the confirmation of my response to the survey where I finalized the details of my order/pledge does.
Which Kickstarter version of Shenmue III would you like?:
Physical Steam Disc (Kickstarter Exclusive Case)