For Intel 1700 I only know of the ASRock Z790 Taichi (the Z690 model also).
I expect it’ll only be found on the most expensive boards unfortunately and note the downsides, lose some M2 slots - although it has loads.
You may not need 8x anyway if you use a PCIe 3.0 NIC, 3.0x4 is 32GT/s (almost 4GB/s) in each direction, plenty for dual 10gbps.
I’m sort of in the same situation, but not sure if the dual 8x could be useful for 25Gbps etc in the future on the other hand the Z790 is 2-3x more expensive that the more basic boards with 16+4 and 2 or 3 M2 slots.
I’m not sure how common bifurcation is on Intel boards, but it could be an option, I worry about risers/mounting the cards though without blocking other slots.
PCIe is forwards and backwards compatible, so you can use a 3.0 card in a 2.0 slot or vice versa but if the board doesn’t have physically 8x or 16x slots it can require opening the end of the slot.
A lot of 10gbps NICs are 3.0 8x, but I think that is likely so that they still operated at full speed even in 2.0 slots which were probably more common ~10 years ago when such cards were new.
Apart from boards with two x8 slots it could be an option to go with a cheaper 16+4 board, HBA + NIC. With the HBA in the future you could add a SAS expander for more drives plus there are the onboard ones - some expanders can be powered via the PSU and don’t need a PCIe slot.
For the sake of $100-150 I would probably go with a board with two 8x ports, it gives more flexibility in the future such as the option of a second HBA instead of an expander.
Looking into the ASRock Z790 Taichi Lite and it’s predecessor a little more feature/spec wise it appears they are identical and the difference is cosmetic, losing some RGB and heatsink mass/covers.