I guess you're saying that you'll only build MVCs for cash, but then will consider joining as a cofounder afterward if the project looks promising and you can work out a fair equity agreement?
But building a MVP together before jumping into a full blown partnership is also rather important in terms of finding whether there's a general fit in working together, you're actually able to deliver on the non-technical aspects of the project and so on ... MVP's are also incredibly good at confirming assumptions about the market.