Hi Gareth,
Well, the back-story I guess comes in a few parts:
Firstly I've become more and more aware that having been very comfortable with what was happening in the themes forum and themes generally until we moved to bootstrap, I've been feeling less and less comfortable with some of the 'advanced' themes like essential, LESS itself (I prefer SASS) and so on over the last few months and for me, the best way to improve that familiarity with bootstrap, less, and the newer breed of themes is to get in there and do it. And I wanted to do it with BS3, because I think we do need to be pushing that way as I think it offers so much more ontop of the benefits of BS2, hopefully Moodle core will move that way in time, even if its not happening yet - Bas has shown how it can be done anyway.
In the second instance, I've had quite a lot of requests to update some of my previous themes - particularly flexi_ii, but also the mutlilayout theme I created a few years ago that allowed an admin to select layouts from the interface without adjusting the config.php or the code - but when I really looked at it, although flexi itself wouldn't take too much to get it working on 2.8/2.9, its hardly what I would call the cutting edge of theming any more and certainly doesn't take advantage of any of the newer user benefits, so wanted to look at the options for settings without creating a dozen setting pages.
Thirdly is something I've been looking at for a long time and have posted about and made experimental themes before (including themes Ive used on my own sites where I could control the browser I was using) and that is the flexbox layouts. I know IE9 is still in use and doesn't support flexbox and my decision not to include full fallbacks for IE9 mean that the theme may have limited appeal/use, although fallbacks are there for any browser using prefixed code or legacy versions of flexbox. Wanted to build something 'mainstream' using it.
Also, as you know from the forums, we often get queries about 'how can I reuse such and such feature in my theme' so I wanted to see if I could take a more modular approach to adding some of the features into a theme, so I can point at it and tell someone exactly which bits to lift out and reuse and how. That can already be done with some features and some themes, but not all. It's kind of like the tiles/includes conversation we've had previously I guess. I was tempted to take things completely out of the lib folder or renderer folder or settings folder and actually add them to a 'carousel' folder, or 'marketing spots' folder and use the includes to point to that to make it even easier, but I haven't got to that level yet (although I might before finally releasing). Some of those features have been around for a long time - I first built the awesomebar into a theme very shortly after Paul orginally released it, while Mary and I worked together on a client theme that included a carousel/slider for something like Moodle2.2. Some of them have only really come into being with the advent of bootstrap. And, as with so much of what I try to do, my main aim is to make these features as easy as possible to use - and reuse in other themes.
As for where I want to take it - well that depends on the users. I'd like to add to the settings without taking it to the level of the old flexi_ii theme as we now have more extensive use of customCSS and I've added the customLESS field in there too. I also want to work on the documentation of the theme as something for both users and developers - along the lines of Easy.
One other thing I'd like to do is package the theme up with some other plugins such as filters (some of which I've already created in work) that would allow users to use bootstrap3 in the editor - a bit like the bootstrap elements plugin I guess - wordpress shortcode style.
But I'm happy to be guided by what users want - what makes it as popular features of other themes, or other systems like WP/Drupal/Joomla.
And if I'm really honest - the ultimate kickstart to get me going on a theme I've been promising myself to write for about a year? I'm getting paid for it! Including full permissions to develop it exactly as I want (so long as they can put their own colour scheme and logo on it) and to release it fully to the community 
Rich
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