I'm surprised with the amount of gloom around Twitter, as I feel like there are some fairly obvious ways they can improve the core product, and with the recent management overhauls, a distinct chance it will happen.
Would these future innovations alienate their userbase? Well do we have evidence they alienated the userbase previously. I doubt it.
While we can point to scores of #ragetweets about how Twitter is finished, finished, because they have replaced hearts with favorites, those complaints last about 2 days. Another example would be how embedded images would destroy Twitter (people said the same when Mosaic introduced images to the web in around 1994, as far as they were concerned, the internet had jumped the shark).
The fact is, Twitter has managed to slowly add features like hashtags and images without changing the essence of the product, engaged users will stick around if they keep doing so. I'd acknowledge that the one last negative sentiment was one close to HN's heart - the developer/API issues - and they still have to iron that out (so far, @Jack's #HelloWorld initiative from three months ago hasn't yielded). But I'm thinking more about features they can add to the core product.
Fairly obvious, and I think impactful, innovations we will see are:
* Long-form tweets - The 140 limit is confusing to Twitter newcomers. Meanwhile, Medium shows the power of a clean publishing platform where anyone can say something important without having to setup a blog and feel the obligation to keep posting. It helps them find an audience. Twitter has a giant ready population of people with interesting things to say and many of them are already using Twitter to say it, in less than ideal ways (too-long Tweetstorms, screenshots, linking to pastebins and 3rd party long tweet services). Designed right, I think they can introduce this with minimal impact on the normal experience and suddenly become a giant source of substantial content.
* Video - Similar argument to long-form tweets. They have a ready population of potential video makers and can easily find videos an audience. I imagine a lot of people discover YouTube videos from Twitter now; those could be directly served by Twitter in the future.
* Curation - Twitter's model of showing every tweet from every friend is archaic and doesn't serve the needs of most users. If I haven't logged in for 2 days, do I really need to see a blast of trivial tweets from 5 minutes ago? They have made some attempts to improve this (e.g. "While you were away" highlights, which so far are mediocre), but can do a lot more, e.g. showing most relevant/popular tweets from friends (see: Nuzzel) and going beyond just friends' tweets/retweets if something is relevant enough. I know moving to a Facebook-like filtered stream will enrage some hardcore users, so they would need to do so carefully and maybe with settings to keep it the old way, etc. ... but I think it will be a big quality boost for most users and also make native ads more effective.
* Apps - The official apps aren't exactly loved and lack consistency (e.g. Tweetdeck and several other official apps still can't render polls, an important mainline feature for a while now). A savvy product team could improve these across the board.
There are a lot more possibilities, and those are just features related to the core product, leaving aside monetisation opportunities such as buy buttons. Twitter has already moved in some of these directions and the signs are @Jack is intent on accelerating that effort.