So I went ahead and tried 5.0-rc1, playing video with chromium to put some load
on the gpu. After few hours it froze again.

[ 6603.232849] nouveau 0000:01:00.0: gr: TRAP ch 4 [00ff8a9000
systemd-logind[1385]]
[ 6603.232865] nouveau 0000:01:00.0: gr: GPC0/TPC0/MP trap: global 00000000 []
warp 3e0001 [STACK_ERROR]
[ 6603.246125] nouveau 0000:01:00.0: gr: TRAP ch 4 [00ff8a9000
systemd-logind[1385]]
[ 6603.246137] nouveau 0000:01:00.0: gr: GPC0/TPC2/MP trap: global 00000000 []
warp 3d0001 [STACK_ERROR]

I then logged in via ssh and chromium was running with 100% cpu. After killing
chromium the log went a bit further, but the screen did not recover and stayed
frozen.

[ 6758.631306] nouveau 0000:01:00.0: Xorg[6494]: failed to idle channel 8
[Xorg[6494]]
[ 6773.631329] nouveau 0000:01:00.0: Xorg[6494]: failed to idle channel 8
[Xorg[6494]]
[ 6773.632334] nouveau 0000:01:00.0: fifo: fault 00 [READ] at 00000000000c2000
engine 07 [HOST0] client 06 [HUB/HOST] reason 42 [] on channel 8 [00fec69000
Xorg[6494]]
[ 6773.632347] nouveau 0000:01:00.0: fifo: channel 8: killed
[ 6773.632352] nouveau 0000:01:00.0: fifo: runlist 0: scheduled for recovery
[ 6773.632366] nouveau 0000:01:00.0: fifo: engine 5: scheduled for recovery
[ 6773.632378] nouveau 0000:01:00.0: Xorg[6494]: channel 8 killed!