Well I wish there were some more solid rumours, I'm looking to buy one in Feb but don't know whether to hold of until March which is what most of the trashy 'tech' news feeds seem to be stating as a likely release. Or would we have heard something from Nintendo if it was to be released so soon?
It looks like production is going to start Q1 so you should be looking at, maybe E3 time for launch in June or just prior to it.
"Nintendo launched Switch Lite with friendlier pricing in late September and significant increases in its overall Swtich console sales in the three-month period ended September 30, 2019. Now the Japanese vendor is reportedly planning to launch a new Switch model in mid-2020, with volume production for the new device beginning in first-quarter of this year. "