Well. Looking at the fact that (in the UK at least) lots of aircraft have the following.
1) A compass it's a legal requirement so all should have it,
2) ILS, LOC and VOR kit,
3) GPS
4) IRS (or INS for the oldies)
The first one MUST use magnetic north. Like my Cub this is all I have. An aircraft with 1 and 2 MUST still use magnetic north as this is how the ground installations are set. Till those are adjusted this aircraft has no choice.
Aircraft with 1,2, 3 and 4 have the luxury of alternating between magnetic and true. However if systems 3 and 4 fail they must revert to magnetic. Not only is it traditional to use magnetic north it's the best practice.