The most successful guitars seem to be not too way out, pretty normal looking, with style and generally appealing to look at. No wonder the Strat and LP were so successful. Any new guitar designs, if they're also not going to be way out, are going to be subtle variations of these well known guitars. So really, most (normal, not way out) guitar shapes have been done. I don't think there's anything wrong with new guitar designers being influenced by the classics.
And I think it's worth noting that, in my opinion, that the success of the Strat and the LP and Tele was surely down to the shape of these guitars and nothing else. Obviously build quality and sound of the instrument is important, but this is assumed. So I reckon a nice new fresh guitar shape, if someone was to design and produce it, could be very successful...and the shape is what will do it.
....I look forward to making my first million....!