My opinion is this. If you end up making a level 20 game, you can always make the DLCs epic levels like previous DnD games. I think it would be a shame to limit their levels to just 10 and I think level 15 is more likely than getting to level 20. I am not sure how much they changed from 3.5 to 5E in experience points awarded for leveling, but getting to level 15 isn't a walk in the park. The first 6 levels usually fly by pretty fast and start to slow at that point. So I think level 15 is feasible considering how fast Act 1 gets you to level 4 and 5. I would not mind if they got to level 20 though as long as everything is well vamped out and balanced.
My main worry though is that capping levels is that if you cap it you get the same problem with waiting on a DLC as well. No matter where you cap the level at its going to be the same problem. You hit that ceiling. This is where DnD has always had its problems in the leveling system. Level 20 is usually the cap, but for computer games leveling caps are just the death of them. That is why in 3.0 and 3.5 they had epic level handbooks made (and I'm sure 2E had this as well, but I'm more familiar with the 3.X line).
To bring up the old Neverwinter Nights line, the DLCs literally propelled you into epic levels. So I understand the hesitation by many in the community to not want to get to level 20 too fast, but game designers should always take it as a challenge to well take up the challenge to progressing forward and beyond. Also remember it takes more and more XP over time as you level. So yes, your level 20 is mowing down armies like they are a joke, but the higher level you get the more older and higher level opponents you are attracting as well. Faerun is filled with large amounts of powerful entities and organizations that can and will offer a sizable challenge to higher level foes. Also remember the Planes of the Multiverse are vast and Mind Flayers are not low level threats. You could be fighting them forever and still never reach their most powerful opponents. Then you also got the Gods/Goddesses and other planar god-like entities to deal with.
I think mainly why most, and I totally understand the hesitation and reluctance of doing high level gaming in DnD, is that it can be really overwhelming to think of something to challenge high level heroes/anti-heros/villains. They can have followers, mass armies, castles, floating cities, and etc all in Faerun alone. That is even before you scratch the Planes which are even more insane.
Anyways, *cough*, I'm rambling. My apologies. Back on topic I think we will more than likely get to level 15 at the current level at how fast xp and acts are going. Which I, for one, am totally okay with, but I would also be fine with seeing level 20 game play as well. Having a target level for a game is fine, but shouldn't be a hard cap if you feel level 20 can be reached and still provide an amazing story and gaming experience.
