I've been planning my build and what perks I'll take and at what levels, within the scope of knowing what each perk does and based on fair speculation of what the others do. In doing so, I've discovered the realities of just how long it would take to really buy every perk a player could conceivably want. While it's well-known that it would take a long, long, long time to get everything, seriously try to plan a build. You'll be faced with the reality that you can either max out a few things and be super-focused on particular areas or spread out & be a jack-of-all-trades, master of none. In order to go beyond that, you'll need so much experience that the grind would be unbearable. Judging by the way previous Bethesda games have been, it just wouldn't be a feasible use of one's time. This isn't an MMO, where enemies are absolutely everywhere & constantly respawn so that you can grind; this is Fallout, where the opportunities for XP are boundless, but the opportunities to grind for said XP are rather limited.
To put it frankly, the purpose of no level cap appears to be to allow players who have reached their optimal build to still be rewarded for gaining XP. In order to create a fully maxed-out character, or even one that's a master in several areas, it would take so long as to be pointless. Unless the game awards you a ridiculous amount of XP or the amount required to reach higher levels doesn't increase substantially as you go along, I just can't imagine anyone doing it purely by happenstance. You have to want it and go for it, so the people saying they hate no level cap because they'll become maxed out strike me as being a bit hyperbolic.