I think some people see this as professional studios stepping on their toes, and have a "I'll have none of THAT thank you very much" attitude. The way I see it, done well studio mods would be similar to the professional mods made for Neverwinter Nights: sure, some of the free mods were just as good, but the premium mods extended the support life of the game, as it was still demonstratively profitable, they brought new tools to the community as these tools were made and released due to the existence of the premium mod program - and they were pretty cheap if you chose to buy them, something in the order of $6 if I remember right. In the end, the premium mod program comes down to a simple choice: like any mod, if it looks like something you'd enjoy, you play it. If not, you don't.
As for leasing the engine, have at it! Push it to the limit, please... maybe the fact that some of our mods are such high quality will push studios to new heights, to justify their project's existence. But any new features that add to the game experience, I welcome, whether they come from a professional studio of one of our excellent modders. I just want the best MnB I can play, since I love the game.
And besides... it makes me smile a bit to hear that Armagan and Taleworlds are making some mullah off this project. He began this so many years ago now with just the hope that he could create a great game and faith that there'd be a market for it... he's earned this - and while I won't buy anything I don't think I'll truly enjoy, I'll at least take an earnest look at any project that continues to expand on and support one of the only games I play anymore.