I don't think anyone is thinking of fitting glass cockpits to these aircraft, the new radio would only be what is required to meet international requirements and FLARM is cheap and all these things are not part of the current contracts.
The G109 engine requirement depends on the availability of engine parts in the short term, in the long term a retrofit is required. I don't know what the parts holding of the RAF for the current engine and things will depend on that.
From the efforts that SERCO & Marshals are putting into the G109 it would seem to indicate they have an adequate supply of parts for the near future.