Well, as 'Modular' has been something that I've been involved in for some time - perhaps I should try to give some insight of where I am with my own efforts in this area. For those new to this subject, I should probably give some background. We've recently talked about "Track Alternatives" in another thread and I've been working on those for a while now.
My first attempts were long, thin ply boxes with track built on top. They could be bolted together end-to-end and for a while I toyed with various methods of doing this, before realising a simple 'hole and bolt' was quite sufficient in G3. My Mk1 modules were intended as test track but started getting used in a 3-tiered display at exhibitions.
I then discovered Spur II, their track modules and photos of their annual GTG in a very large gym, which they were filling with track and stock. It seemed a good idea to use their experience when developing a G3 modular system, so the M01 'standard' is very much based on the Spur II standards.
A quick word about 'Standards'. Standards occur naturally when enough people decide to adopt the same approach to something. In many cases, they are pretty arbitrary in nature or perhaps copied from a popular design. In many ways, what particular dimension or fixture is used doesn't matter too much, as long as everyone uses the same ones and that they make general good sense.
The lastest version of M01 was published in early 2011, having been slightly modified once or twice before that. I believe it to be a perfectly workable system (and the Spur II version is widely used in Germany) but it has not been taken up within G3 generally (with one or two notable exceptions). To try to encourage (kick start) module use, I designed a kit that met the Connect 3 standard (e.g. to the M01 standard) and had thirty kits made with the support of the Society. Thanks to the support of other members, they were all eventually sold (we had sold the required 'break-even' quantity before we placed the order though). At £25 each - they were about one third the nearest equivalent baseboard available from commercial suppliers in the smaller gauges.
Since then - well a few dedicated members have made progress with their modules but (especially when compared to their use within Spur II) they have not been a great success. I have thought long & hard about this and have come to some general conclusions about the reasons for this difference in uptake. It's worth covering briefly I think.
Spur II is actually a 'Scale' that is modelled in five gauges (Standard, Metre & Narrow Gauge 'Feldbahns'). It is generally 2-rail in nature and highly 'scenic' (in the traditional RM sense) in nature. Whilst I'm sure they do "outdoors" it doesn't seem to be their focus. In terms of commercial support, obviously a big driver of Spur II would have been LGB (1:22.5 on 45mm). They have united their various gauges through their use of modules (which are not quite so restricting in Feldbahn size anyway) and the standard LGB 'G' scale.
Gauge 3 're-emerged' directly into the garden because most of the Society founders were 2.5" live steamers (although not exclusively). As more traditional railway modellers joined the gauge they brought their existing RM practices with them in terms of scenic modelling but also their approach to baseboards (and exhibition railways). The idea of 'interconnecting' different layouts is not common (although modular is now very popular in the US from 'N' gauge upwards).
In summary, a G3 modular "Standard" exists that is very similar mechanically to the one used by Spur II. Whereas the need for a modular system seems to have been recognised in Germany, probably the availability of traditional garden and exhibition tracks in the UK has resulted in less demand for an alternative system. However, I've believed for some time now that one of the biggest 'barriers-to-entry' into Gauge 3 is the availability of a modular, scalable and practical alternative track system.
I have to take a phone call but I'll be back! (Arnie-like) with a second part.
YOU CAN WAKE UP NOW MIKE !!!

Regards,
IanT