I wouldn't bet on this:
- The lifecycle on the market for a smartphone has shrunk to 9 to 12 months for the last two years. The Xperia 10 was introduced by Sony in early spring 2019.
- A typical sign of devices being EOLed is that Amazon themselves stops selling them (i.e. only "Amazon marketplace" sellers remain): This is already the case for the Xperia 10 and 10 Plus.
- It already becomes hard to obtain the Xperia 10 Plus at the Amazon marketplace at all (new and for a reasonable price).
- The "final" price at Amazon (marketplace) for its predecessor (the XA2 series) was ~€200,- for the regular model and ~€300,- for the "Plus" model, before it stopped being widely available (in late summer 2019). This is where the Xperia 10 (<=€200) and 10 Plus (<=€300) are right now.
- I expect the recent release of SailfishX for the Xperia 10 to slightly speed up selling the last devices in stock (in Europe).

Hence you might be better off ordering one now.

P.S.
What frightens me a bit is the announcement of a "great announcement" in early 2020 WRT future devices and the future of SailfishOS.
The last announced announcement (originally in the monthly Maemo-IRC community meeting) was about the "future" of Linux (kernel) and AlienDalvik on the Xperia X, and the final revelation last week was quite a disappointment after weeks of keeping users anxiously waiting for it. And this was just an announcement, not a "great" one.