Hard to say, but I imagine that prices should hopefully come down a fair bit over the next 12 months as production ramps up on other 4k IPS panels like AU Optronics AHVA 28".
Personally, I'm waiting for a 28"+ IPS-Type monitor with FreeSync compatibility before planning to upgrade from my old (2008) HP LP2475w. And tbh, the 4k eco-system doesn't seem quite there yet: i.e. due to the current scarcity of G-Sync and (lack of any) FreeSync capability; HDMI/DP bandwidth issues limiting refresh rates; IPS panel production still ramping up, plus the prerequisite of needing an exotic GPU set-up to get playable framerates at 4k resolutions.
The whole prospect should be a lot clearer next year with next generation GPUs, improved panel production and competition, wider G-Sync and FreeSync prevalence, etc. That said, the 31.5" IPS Sharp IGZO panel 4k monitors have come down a lot in price in recent months as you noted earlier (now £1500-2000), whereas they started out around the £4000 mark at launch IIRC so the downward trend is there.