I think you should run far away from emphasizing the matching of a core to it's most cost-effective target -- it's not something you need to do until you actually have something nearing the need to buy a shitload of parts and ship. You generally develop on one of several overpowered dev boards that you already owned. Pitch the multi-hardware parallel build as testing, not chip selection: 'what targets is my build not totally broken on'.
When I was doing some rather oddball FPGA development (trying to do Alan Kay style pedagogical CPU dev) I would have killed for this. I was attempting to build stuff with as little HDL as possible for clarity purposes, and would frequently fuck myself over when the Xilinx tools couldn't synthesize or place-and-route it anymore for my Spartan-3 hardware. Some of it was just their incompetence, where a hand-laid design could fit easily, but a lot of it was just classic traveling salesman problem woes. It would have been a lot easier to see what the real constraints I was hitting if I knew which chips it didn't work on anymore.
The vendor compiler toolchains are fucking dogshit. Just having that hosted and guaranteed not to collapse in on itself would be golden. You should also develop simple desktop software for flashing the builds for at least Linux and Mac OS X. At one point I wrote my own flasher from scratch that sucked but Xilinx's Windows flasher had shat itself on me and I couldn't get it to work again (the Linux stuff never worked at all, ever). Make a simple drag-and-drop flasher. You could even sell a rebranded USB-JTAG that's guaranteed not to suck.
Simulators are ridiculously awful, but you're not going to come anywhere near fixing that.
"that the user ends up buying and using the most suitable hardware" is a side effect of some of your features, not the real use case you should be selling. It feels somewhat greasy, because at some level you're just marketing hardware to me. Even if you do try to monetize that through some kind of affiliate thing, don't put it up front. You'll spook the engineers.