Those usages may have been phased out as a part of the Lift 3 release and we forgot to clean them up. If you can confirm they’re no longer used we would welcome a PR that cleans them up.
With regard to your Twirl template, using an InMemoryResponse or XhtmlResponse would be the best option. Lift and Twirl are not designed to work together — I’d even go so far to say that our opinion on how web development should work is greatly at odds with Twirl’s — so I’m not surprised that the interface there is a bit awkward. You may be able to write your own subclass of LiftResponse that makes it a bit better.
With regard to the note about lift responses: I’d welcome concrete examples or improvements you’d like to see. Lift is far from perfect, but without specific examples it’s really challenging to try and address your concerns.
Thanks,
Matt