The issue with T3 and accommodating FR/BE/U2.
T3 for S17 will have 19 stands, to which 5 are domestic gates (latter obviously beneficial to Flybe)
Then consider for S17 Easyjet will have 12 based, Ryanair 9 based and Flybe 10 based (with multiple other overnighters).
If we then consider growth scale in a mediocre scenario for the next 10 years, it's not implausible to consider Easyjet at 18-20 and Ryanair could have about 15 based.
That means T3 would need about 40-45 stands, and there just isn't the space for that kind of build (MAG love car parks so unlikely to get rid of the nice big money earning car parks near the terminals).
Therefore, seems unlikely to see both Ryanair and Easyjet in the same T3.