This is brilliant. Super easy mental model. Super easy to use (just drag and drop!). No friction. This is going to be big, whether it's you guys (hopefully!) or someone else that steals this idea (boo!)

And I wouldn't pay too much attention to the Windows/Linux users in the very early days if it's too much of a development burden. There are tons of tech forward companies that are mac-only that are a large enough market to build momentum.

If the windows/linux people want it make them put their money where their mouth is and charge them in some way. It costs nothing for them to say "Build this for me!" but they already have enough info from the demos and mac app to make a purchasing decision. So if they're serious get some money from them. If you do a pre-order and say "if it's not released in 3 months you get your money back" that should be enough signal to know if they really want it or not.

Congrats! Not many people make something this good. Now don't screw it up :)

And if you're not part of YC already you should do a late application for the W20 batch.