There are some micros that are earlier than others. Red Robin, while being the prototypical micro tomato, is not necessarily early - as has been noted.
The particular project Diane, Dan, and myself are working on is an umbrella project with the main intent to diversify micros. It is composed of smaller, more focused projects. Currently there are two active sub-projects that Dan has initiated.
MMF - Massively Multi-Flora
BLT-Worthy - Enhancing flavor and size in micros
MMFThis one has had much more progress. Dan was participating with ChrisK, who was developing a particular MMF micro variety. ChrisK allowed Dan to use that variety as a parent in any number of other crosses for Dan to work on independently. First, Dan was focusing on developing more micros with the MMF trait - so we now have several lines that explode in hundreds of flowers - but we're still developing these.
BLT-WorthyDan's goal here was to develop micros that produce tomatoes that taste more like big meaty indeterminates, and are big enough you can make a sandwich with them. Please note, we don't believe it likely we're going to grow 12oz tomatoes on a 6-inch plant, but we are showing that you can grow bigger-than-cherry tomatoes on a small plant. From our notes, I believe Dan has grown up to 6oz tomatoes so far (on a F2 - don't see notes on plant height for this one). I see several that hit ~3 oz on plants closer to 12-16". I have a ~6" plant now with a beefsteak shaped fruit that measures around 2-2.5" in width. We'll see weight once harvested and whether it tastes any good.
There are already several varieties of "micro" tomatoes out there, with many available via Heritage Seed Market. However, many don't taste very good, and many also have very thick skins (so much so that my wife has to spit them out).
One area micros do well in though, is indoors under lights. This allows one to produce some level of tomatoes during winter, in a spare room or garage, if for nothing else than to have a decent addition to salads

Currently, we have some ~159 crosses Dan has made. The majority are crosses between that line from ChrisK (at the F4 and F5 generations) with various other tomatoes - many indeterminates. Dan has also then taken some of those results and crossed them with each other.
We're still quite early in the project overall, but we are definitely finding some very interesting combinations, and it seems we're finding some very tasty tomatoes
