It would technically work in the sense that you'd be pumping in heat at the higher efficiency of the minisplit. I fear though that you'd never quite be happy with the feel as the benefit of the hydronic in-floor is consistent temp radiated throughout.

If off electricity the 'standard' way - not uncommon in Europe - to get what you're after would be e.g. an air to water heat pump (or a ground source). It is more expensive of course and I understand may be hard to find in USA (although you say C so maybe you're not there?). In coldest outdoor temps you would still be running off of electric resistance heat (you could possibly keep your current boiler as backup).

Because target output temperature not very high for infloor radiant, it can be reasonably efficient, but depends on your climate too.

Too many issues but I'd not rush into your minisplit approach. Air to water heat pump would at least be in line with original design.

There are newer tech solutions being developed (e.g. CO2 heat pumps, 'big in Japan' as they say), but not yet common or widespread.