So, in regards to the original post, I have two main ideas regarding the general direction of the sequels (yes, plural!) to PoE. First off, I think it would be neat if they happen Elder Scrolls style where each game visits a new region of the world setting. (To be clear: I want to stick to 2d isometric view and tactical combat, or even possibly a grid-mapped turn-based strategy spin-off; the Elder Scrolls reference in no way implies any desire for a 3d first person game.) If PoE2 visits the Vailian Republics / Old Vailia, then perhaps PoE3 would visit Rauatai or the Living Lands, etc. I suspect they will want to start over from level 1 in telling such stories, and this may be wise to smooth over any lingering issues with game balance, the XP curve or the lack of high-level spells.
However, I have a neat idea: so, for starters, PoE2 is a game which happens concurrently in the timeline with PoE but in a different location. Then, when we get to PoE3, you can import your character from either PoE or from PoE2...
Seriously, how cool would it be for the Lord or Lady of Caed Nua to meet up with someone who has been through a different group of world-shaping events from another region in order to meet a new threat from another part of the world (perhaps Readceras)? They could balance the power of having 2 "charnames" in your party by causing both characters to lose all of their money and access to their original-game stash (if you only play one or the other, they get the benefit of access to their past wealth; and if you make a brand-new character, perhaps there is some other benefit to offset your loss of not importing a "charname," such as giving a new character some unique items based on a past history you whip up during character creation).
Well, just a thought. There would be some benefits to waiting one game for a BG2/Throne of Bhaal-style game, such as having extra time to smooth out any remaining problems, flesh out their setting further, create more spells to populate the class spell lists with, and in general feel extra-ready to tackle the fun and problems that come with "epic levels." I think they must intend to visit level 20 someday, based on the clues in the spell progression table, and I wouldn't be surprised if we see a game that takes us higher, say to level 24 or 26. Personally, I don't mind if we keep getting reset to level 1 with each new game, but I wouldn't mind if the level cap were more of a practical limit based on how much XP exists in the game world rather than a hard number (like one of the previous posters mentioned, I enjoy a game more when I feel my character is still advancing and still improving rather than becoming largely static in abilities and power). People like me who are completionist would get a slight edge that way, but it shouldn't be necessary to enjoy and beat the game.