"2. All sampled instruments to be played by the same artists.."
That would cost a lot more for the artist to hang around recording samples than PG doing it themselves with the same instrument, and have their own PG sample player vsti.
Like Shots n Holds they are just played with the same instrument by someone at PG I would say as they were an added features after realtracks.
Having Direct Input guitars is good as I can get a RealTracks artist to play most then use the same DI guitar in Kontact to create the solo I need. You can use something like https://www.kvraudio.com/product/redshift-pickup-replacer-by-acmebargig
to get the same tone.
Yes have a PG RealInstruments sample library created from the existing RealTrack Instruments.
This way you can fill in sections that the RealTracks could not give you yet play seamlessly.