Should I buy one though if I am going to use it for a years in a row without any modifications
I don't see any problem with doing so, sure.
Many AIBs use reference PCBs so you can still add a water block if desired.
Ehh, yes and no. It really depends on the vendor:
http://gpu.watercool.de/WATERCOOL_HEATKILLER_GPU_Compatibility.pdf
People don't plan for it in advance; most of the time, it's on a whim - I'm not including the liquid cooling enthusiasts here. They already know what the heck they're doing.
Say a user buys a nice air cooled card - let's use the 2070 Super FTW3 model - and suddenly, they want to custom cool it, but then run into the nightmare of finding a block that fits, because the RTX 2070 Super waterblock they bought didn't fit, because they also failed to notice that the block was for a reference card, and they didn't know that the PCB on their card was custom made.
I've seen that happen a few times; some people just dive right in without consulting the right people and end up screwing themselves over...