Another great article from London Reconnections here:
https://www.londonreconnections.com/2019/crossrail-getting-a-grip/
Looks like 2020 will be the earliest. Huge problem with NR needing to reconfigure platforms 16-18 in Summer 2019 for longer trains - and potentially Liv St Low Level will be used for Shenfield trains and then reversed!
Doesn't really make a lot of sense to me. If you can run the trains through the tunnel at all, why stop at Liverpool Street? If Farringdon station is due to be handed over in the Spring and that work's scheduled for the summer, you may as well terminate them at Farringdon and get some utility out of it. (assuming Fisher Street crossover is west of Farringdon station, if it's underneath the street of that name I imagine it is but I haven't seen the track diagram).
The TfL Rail peak service may not be as intensive as the full Crossrail core service but it's busy enough that the signalling system will have to be operational down there. Given we're supposed to have a full year of testing ahead, I can't see that being very realistic. I'm not even sure it'd be safe to send them west of Stratford down there to turn around empty with no signals.
Personally I only see two outcomes - either the Liverpool St remodel and all projects reliant on it slip back a year, or it carries on regardless and for the few months it takes to complete the TfL Rail peak service is reduced to 6tph terminating at Stratford with replacement buses in continuous operation to supplement the service frequency via Newbury Park as they currently do during engineering works. I think the former is probably more likely.
The other possibility is of course that the December 2019 PRM derogation doesn't happen and with a large proportion of Anglia services suspended until new rolling stock arrives, 345s get clearance to use platforms 8-14 at Liverpool St as well.