IMO at this stage it doesn't really matter if the next version is called 0.5.0 or 0.4.15.
As far I know, the meaning of the version number is not really defined, not even vaguely.
The difference between the 2nd and 3rd number seems to be non-existant.
So the choice of whether the 2nd or the 3rd number will be increased will likely be pretty arbitrary.
And it will stay this way as long the meaning of each of the numbers is defined.
I can only guess the 2nd number is for “more significant” changes than for the 3rd number. But what constitutes a “significant” change will be very subjective.
On GitHub I found the milestone “0.5”:
https://github.com/minetest/minetest/milestone/5I am pretty sure 0.5.0 will not be released for sure as long any issues are left in this list. So maybe the 2nd number in Minetest is reserved for some minestone-kind type-of-thingy. The milestone also mentions possible incompatibilities, so this suggests another criteria for increasing the 2nd number. But this is all just guesswork from my side.
As it stands now, the Minetest version number is mostly just there to identify which version is newer. Not less and not more. And any discussion whether to increase the 2nd or 3rd number is pretty much pointless at this stage. Also, I think users should normally not dictate version numbers. Unless the version numbering system is really fucked up, maybe. But this is clearly not the case for Minetest.
This is not an “official” developer opinion, but this is how I see and understand it.
What is much more important is consistent numbering. E.g. it would be very bad if Minetest developers suddenly release version -34.249a+build-a4fde40. ;-)