I’ve wanted a fretless guitar for a long time - still thinking of pulling the frets off my cheap strat, but I’m not sure I’d be altogether delighted with the results. Fretless acoustic guitar I hadn’t considered, but here’s the Turkish composer Cenk Erdogan showing how that might work out:

Apart from the mechanical difficulties involved in playing such an instrument, I think I’d have some real trouble getting my ear round the possibilities of non-even-tempered scales…