the end of trackmaster!?

yet the "tie in" i think we are both referring to has been over a year.
so... where is the "tie in"?

There was a tie-in known as the Scrapyard Escape Set for Journey Beyond Sodor in 2017, and this year's was the Turbo Jungle Set. Next year, there isn't going to be a movie but there will be 3x20 minute specials, so presumably there will be something carrying the theme of these specials.

The Super Station was a big notable occasion in 2017 for its size and being the first item to be compatible with multiple toy ranges that I can understand it overshadowed the movie tie-in products.

if TrackMaster ends, this should be Tomy's chance to replace them with Plarail in the US and UK Market.

It would only happen if Mattel wanted to grant Tomy with a global license, and I think Mattel would rather dominate the market with their in-house products.