I likewise thought I had found a purple skinned Tediore ETech launcher before, but if so it was so long ago that I don’t have a screenshot of it.
As of right now, not only do all ETech launchers spawn with blue rarity material, but the game will autodelete any ETech launchers that are “given” purple rarity material upon launching.
Likewise, attempt to “give” a purple launcher the blue materials that they used to spawn with, and upon loading the game you will see the material has been converted to the proper purple skin.
I have not managed to find any non-elemental ETech pistols since the patch, but they are still allowed in game and thus should be able to spawn.
I’m just a person with an interest in bugfixing, and I feel confident these are bugs and ones that could be fixed.