>>Universal Windows Apps can be WPF or HTML/JS.

IMHO the winner won't have the name of an OS in its label. IMHO an interpreted 4GL over platform-specific runtime is going to sweep the field in time. Not sure why it's taking so long- even before Dr Dave promoted the idea, Andy Gariepy was onto it in the 1980s and the decision to focus on Mac followed by some disasters and missteps is the reason most Microsofties never heard of him. I had personal experience on the TRS80 where his ZBasic compiler costing less than $100 produced very tight Z80 binaries a fraction of the size of the TRSBasic source that ran like scalded cats. A modern Andy can transform development and make themselves a fortune- as long as they don't lose sight of the cross platform ideology (or sell to a vendor with a vested interest in a single platform.)