I think Grant Shapps has wanted LO to take over for some time and has been very vocal about it - having once shown a letter from TfL that specifically mentioned more services to/from Brookmans Park (his home station). This was during the 2018 timetable fiasco, when anger was quite high and justified.
I too have 'predicted' this would happen for around 15 years!
However, it seems more unlikely today given the integration of GN inner services with other GN and TL services, as well as the financial troubles of TfL, plus now it seems Grant prefers to travel from Potters Bar and presumably on faster trains. Maybe he's less bothered as he once was!!
We shall see, but if TfL was going to do it then all the changes at Stevenage and the all-new trains, plus recently revamped inner stations, clean tunnels, new signalling due to be done and talk of leaky feeders to provide phone coverage, it seems that they won't have much to spend besides the logistical issues mentioned by others.