Ah that's good to know! I didn't realise the rear brake was internal. Thought it was external on the down tube rather than the top tube.
Caadx seems like the sensible option. Found a caadx disc 105 for £600 online so might go for that (second hand not on sale)
You can try and make it work by replacing the housing with compressionless for the rear, but you'd still need to removed the bottom bracket to gain access to ensure smooth operation,
Rear brake is a big flaff due to running the cable inside the BB30, thus give a very crap modulation.
Only worthwhile if you're going for the hydraulic version.