Cube or Sauerbraten are of minor value. There are a lot of better alternatives, than using this sort of game core, since those listed above are made for arcade games. TC:Elite on the other hand aims more in the dircetion of a tactical shooter with very realistic elements.
Main criterion which is speaking against any sort of standalone or GPU-based release, nevertheless, is, that they do not wish to share their code with any others!
Also cheatprotection, advanced mapping tools and their gathered experience with quake related software is coming in handy, which would cause a big banana skin, if they would change.
If you have always been working with one game core, have the know-how and also achived quite a lot of success (tc:q3), then you might want to stick to the quake-line.
ET's (PLC) product life cycle is still not expired, yet. It is still in the "Cash Cows" period, which means, that it has a huge share of the market, while this other one mentioned above will never pass the "Question Marks" period and will soon be a so called Poor Dog.
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Bottom-line: No one plays this sort of game, while ET has a huge community, which can get extracted with a high quality product as TC:Elite.
Compare the following:
CUBE:
W:ET
