Best not to get overworked about it, I just checked TAKARATOMY's Plarail Website and there's no signs of TS-01, TS-06, and TS-12 being replaced yet for a few reasons:
The "All Engines Go" reboot still hasn't dropped yet.
Japan usually does stuff 6 months - 1 year after the initial drop of something from the Franchise as they don't get it until then due to having to dub it in Japanese.
-- TGD (happened in 2008, plarail makes merch of it in 2009), HOTR (happened in 2009, plarail makes merch of it in 2010), SLOTLT (happened in 2015, plarail makes merch of it in 2016)
We've only had like one glimpse of possible AEG toys with the new Wooden Railway promo, and just a few promos of the main 5 characters on clothing and lunchboxes.
If plarail does go with the reboot and it a success there, their lineup would probably be changed entirely and they'd do another rebrand such as the 1992 - 2002 range -> T Range (2003-2012) -> TS Range (2012-Present) -> and if the reboot doesn't instantly fail TA Range (speculation)
If they did do something like that it'd probably look like this:
TA-01 Thomas, TA-02 Percy, TA-03 Nia, TA-04 Diesel, TA-05 Kana, TA-06 Gordon, TA-07 James, TA-08 Kenji, TA-09 Carly and Sandy, TA-10 Emily
tl;dr: they aren't being discontinued, this is just probably a site error
