Although I totally understand the immediate concern about them abandoning their current early access game and moving to another for more money, I have met these guys personally, and I think I can guarantee that they aren't doing that. Even though Marek wouldn't tell me the details of their new project, he made a point of talking about how they had greatly expanded the team in order to begin work on a new project, specifically to make sure that they wouldn't reduce the quality of Space Engineers. He also talked for a bit about how they had recently hired a small dedicated research team to make improvements on their engine, so they can open up more possibilities for Space Engineers as well as future games. I got to talk to him for a while, and believe me, this is not a guy who is in it for the money, or who is going to jump to a new project without finishing the old one. You can see the passion in his eyes when he talks about his work, and how happy the whole team is with what they're doing. I am definitely convinced that both games will be completed in very high quality, and have no qualms about supporting Medieval Engineers.
Of course, I can only ask you all to take my word for it. Naturally, if you decide you don't want to take the risk of investing in both games, or in either one, that's totally your decision and I wouldn't argue it. I just hope Keen doesn't automatically get flamed for taking this step forward just because certain other unscrupulous companies have caused gamers to lose faith in the entire industry. : (