Not from what I have seen in internal CP7^▸ (Control Period 7 - The five year period between 2024 and 2029) business plans, GBR^▸ (Great British Railways) is very much part of them.  These business plans have been agreed with ORR^» (Office of Rail and Road, formerly Office of Rail Regulation - about) and DfT^» (Department for Transport - about).  There is a lot of work happening in the background to enable GBR by, DfT, ORR, ToC's and NR^» (Network Rail - home page) with the FoCs being consulted.

What is more likely the case is insufficient Parliamentary time before the next General Election to get a Railway Bill through all of its stages, so I suspect the Government will postpone the Railway Bill until the new Parliament.

However you always have make allowance for the politicians taking short sighted decision on a lead up to a General Election. 

The No 10 had better come up with a viable alternative, GBR is being developed by Railway specialist and not politicians so has a chance of working, if the politicians come up with a cunning plan then our National rail system will remain suffer along with the travelling public.

No 10 possibly still has in mind the failed ideology of it all being private sector, private sector has a place in the Railways but so does the public sector