With a web-app like this, I would be concerned about IP issues. Half the industry is banking on IP unless they are open-source like the OR1K. Otherwise, a proprietary house might be hesitant to upload HDL code even if it is over a secure SSL connection.

For simulation with Icarus Verilog, it might be possible to upload the compiled VVP binary. You can sell your computing power as a utility (ala cloud computing) and help people save cost from buying an expensive server and save time from having to wait days for results.

For FPGA selection, I personally doubt that your tool would be that useful because this decision is primarily dictated by the cost of parts - rather than the specific features. The hardware business is very cost-driven. What you can do is to provide customers with the ability to perform synthesis over multiple architectures for the purpose of 'testing' that their code works on them all.