There currently isn't a £700 GPU that provides high framerates at 1440P in the latest (admittedly small number of) titles. AMD cards don't count as they just aren't up there when you factor in upscaling and RT. A 4070 Ti may satisfy a portion of gamers, but it's starting price is £750, and it only has 12GB VRAM, which unticks its use at 1440P for a handful of modern titles that reach 15GB VRAM use (Alan Wake being the latest example). Ultimately this all boils down to the games you play though yeah.
The way I see it, there isn't any roadmap pointing to a 4090 not being still top end even a year after a 5090 release. Yeah it will be cheaper then obviously, but it will still provide high end performance whilst nvidia still charge eye watering sums for lower model cards. There is a chance that NV will release DLSS4 and only support the 50 series with it, it's a chance, even if small. The technology we see now shows strong growth for DLSS3 technologies, and that's the current evolution path with lots of headroom to improve in big ways, all NV need to do, and are doing, is just train the AI model sets just like they have done between Alan Wake 2 and Cyberunk resulting in higher quality denoising and better detail from ray reconstruction, and that's just within the space of a few months.
As for DirectX 13, there's not even any rumours of DX13 on the horizon, not even for Windows 12 coming next year. If they did release DX13 with Win12 as a selling point, then no games would support DX13 for many years unless a dev decides they want to run two APIs to cater to consoles (DX12) and PC (DX13) - How may devs are left that would put that kind of effort in any more?
Plus, remember that these cards are also not just for gaming any more. All major applications now have GPU acceleration with many now coming with AI acceleration (Davinci, Photoshop, Lightroom etc etc) - So for productivity they come into their own too. But yeah whilst the number of games utilising the full scope of gaming engine features can be counted on one hand of these cards, the number is growing, and Unreal Engine 5.x has only just started to gain some traction which will only grow bigger like UE4 did, just hopefully without all the stutter struggles of old.
The new cards all need to be 16GB cards at the minimum. Many games now hit VRAM up to 15-16GB at 1440P if higher settings are used. It's not an option any more so thankfully these new cards are seemingly going to be over 16GB too. The same applies to productivity, Lightroom exports can use up to 22GB of VRAM for example I've found.
I guess the gist of it is if you keep wondering what might be around the corner, you'll never fully enjoy the "now". Price to performance the 4090 is the only card that delivers performance for its RRP. I would never dream of buying one at today's prices though!