I think it is very unlikely DOTA2 will take much from LoL unless they've heavily strayed from the original DOTA.
I think you may be underestimating the situation. Valve is an extremely popular company, and IceFrog has a very loyal fanbase, being the pioneer of the original Warcraft 3 mod that started it all. DotA was ridiculously popular for years before LoL or HoN even came along (in fact, they only came along because they saw how successful DotA was). DotA sort of fell out of favor because the Warcraft 3 engine has become very dated and undesirable (compared to the newer games), but I think many people are just waiting for the sequel to go back to their roots. I personally played DotA for about 5 years before I found HoN and started playing it. From HoN I played LoL for about 6 months (I have over a 1000 games played for all 3 games of the genre), then went back to HoN while waiting for DotA 2. For me, and for countless others I've talked to, none of the "spiritual successors" were ever as fun as the original.
I consider HoN unplayable and for reference, I've got over 1200 normal games of LoL and almost 250 ranked games with a 1300+ rating. Terrible UI, needless complexity, bad basic game mechanics all of which result because it was a port of DOTA. So unless DOTA2 opts for the "same name, different game" approach, I'm not expecting anything all that impressive.
I'm not sure how your expertise with LoL qualifies you to make judgements about another game it seems you've barely played. If you had played several hundred games of HoN or DotA I might understand where you're coming from but it's like saying you've eaten 1000 McDonald's Meals and 1 Burger King Meal and you know McDonald's is better. I used to have a lot of friends who played LoL who hated HoN because the learning curve is so dang high comparitively. In LoL they remove instant-deaths, denying, gold from dying, rune control, teleport scrolls, and many other things that makes it a much easier game to start with. However, every person that has given HoN a chance in my experience (a chance being a couple dozen games or so) ends up liking it a lot more. Most people just don't make it that far (what with the horrible community, confusing mechanics, and no AI support I can't blame them).
I suppose it depends on what you're looking for. LoL is a much more casual game and newbie-friendly, because of those complicated mechanics you mentioned earlier. It is much easier to pick up and learn and play with your friends without getting bogged down with all the details, but because of all this it sacrifices depth. DotA is a complete gauntlet for new players (from everything I've heard, I started playing it when it was relatively unknown), but if you stick with it long enough it becomes a much deeper, more competitive experience. Can you say that either game is better? Of course not, they both have their ups and downs, and as far as I'm concerned, they both target completely different audiences.
* The community in LoL is no worse than anywhere else, and significantly better than most such as the aforementioned TF2, HoN and DOTA.
Agreed, at least that the LoL community is much better than HoN. This has a lot to do with Hon's in-depth stat-tracking in my opinion. As soon as people's ego's are on the line, they start acting like barbarians if they're losing. This is one more way that LoL being a more casual game is its saving grace.
I'm not seeing that with TF2. Now, it's completely possible that I have blinders, because I have literally been playing that game since day one of the beta. But really for a new player, I don't see it being that hard. You point the gun at the guys who aren't your color and press mouse 1 and you've got 90% of the game covered. It has intro videos for all the game types that easily explain what to do. It has giant team colored arrows that pop up on the walls, so even on unfamiliar maps you can generally find which direction you should be running in to find the battle. I'm confused as to what is unfriendly to newbies about this.
I'm also confused about what makes TF2 noobie unfriendly. I guess in some ways all shooters are pretty noob-unfriendly because you'll probably die alot before you get the hang of the game; but as far as shooters go, I don't know if it gets much better for new players than TF2 (I would certainly recommend it over Halo, Call of Duty, or Counter-Strike).