While other people have already answered this question, I'll give you the way to calculate this. First: Find which NUMERICAL season the gear is from. Trials gear obtained this season is S11 updated. Second: Subtract 9 from the numerical season. 11 - 9 = 2. Third: Multiply the remainder by 50. 50 x 2 = 100. Fourth: Add the product to 1260. 1260 + 100 = 1360. So, S11 updated Trials armor will be sunset when the max power cap is greater than 1360.

-trials gear caps at 1310 so season 13. - it (and literally every other armor piece in the game) will be available for transmog. - someone else said there was new gear coming. That’s not true. Bungie specifically said Trials would receive new armor yearly, but that it wouldnt start in season 12. It’ll likely be season 14 ( when V1 trials gear is sunset) that they’ll release a new set.

There is going to be new trials gear in beyond light, if you save the end game bounty then claim it in beyond light you could get new trials gear early. Though I don't know what would happen if you opened it on a Wednesday so I'd save it until first weekend

It is getting sunset in beyond light but not as soon as beyond light releases. We're on season 11 right now with the power cap of 1060; the Trials gear caps out at 1310 and that cap wont be met till season 13. So still very viable to pursue Trials gear :)