In my mind he's gone from "nice bargain trade deadline pickup" to "terrific trade asset" to "someone we might want to keep for a long time"
Some facts for the statistics crowd:
1. On Boston his per-36 numbers are 27.0/7.4/3.1 at TS 59% with a +7.8 net plus/minus. Who knows whether he could sustain such numbers for an entire season (or at higher minutes), but they are amazing.
2. Here are Thomas' per-36 numbers compared to Lillard and Irving over their first four seasons in the league:
Lillard 19.9/6.0/3.7, TS 56%, 18.6 PER, 0.140 WS48, +5.5 net plus/minus
Irving 21.9/5.9/3.7, TS 56%, 21.0 PER, 0.143 WS48, +3.7 net plus/minus
Thomas 19.9/5.9/3.2, TS 58%, 19.2 PER, 0.139 WS48, +4.3 net plus/minus
And bottom line, he's probably the single biggest reason for the C's going from irrelevant to relevant over the last few months.