Well, I bought Aseprite while it was FOSS, and license was one of the reasons I chosen it instead of PyxelEdit. I wound't say I feel betrayed... more like disappointed.
(This is also why I, for a project I'm about to release, am doing an OSS/commercial split with higher-end features not part of the OSS version. But my software is designed for enterprise use, and they're used to paying for things.)