Everyone is free of course to use whatever format they wish. Don’t let me stop you. I got the impression that you wanted a new, additional format added to the Kosmo ‘specification’.
Designing and building and sharing modules using the existing Kosmo format is likely to appeal to more people. That’s all.
That’s not obvious. Of course a 10 cm module will not appeal to someone who has no 10 cm row and doesn’t want to build one or to make a 20 cm replacement front panel for it. On the other hand it may well appeal more than a 20 cm version to others who do have or are willing to build 10 cm rows.
Designing such modules shuts out some people as potential users of them, but only people who choose to be shut out.
I am really glad I included a 10cm high middle row!
I concluded that a case of three full height modules would be too large for me. To make sure I had enough space for all the modules I wanted, I decided to go for some 10cm high modules, particularly for utility modules that you mentioned. This was also influenced by my wish to include some small speakers taken from an old PC speaker set, that look good in a 10x10cm panel. 
I do not think 10cm high modules should be part of the Kosmo standard, as the market for Kosmo is already relatively small.
But these 10cm high modules can be very useful for some DIY utility modules or bridge modules (between different parts of a case, or to connect to external sources).
People make 10 cm modules, and will continue to, and some people will make their extra PCBs and panels available, whether they’re “standard” or not.
What would be unfortunate is if there were two incompatible “tile” formats causing confusion and ill will, as is the case in Eurorack. Putting something about “tile” modules in the Kosmo Specification topic might help prevent that. But then again, it seems unlikely. The reason there are two “tile” formats in Eurorack is because of Eurorack’s confusing non-even vertical dimension. For Kosmo “tiles”, 10 cm is the obvious thing to do and I’d be surprised if there were any trend toward, say, 9.7 cm or 10.8 cm formats.
Anyway, “the Kosmo standard” is almost an oxymoron. My Kosmo modules have slotted mounting holes in disgard of the Kosmo Specification, and my panel component holes and pad sizes are a little different as well. It says gate signals are “minimum 4V, typical 5V?” but we’ve just had a big discussion over the Plexquencer’s 8.4 V gate threshold. Sam gives “2.5cm/5cm/10cm/20cm/40cm/60cm/80cm” as allowed widths but the Kosmo Specification just says “multiples of 2.5 cm” and I’ve made a number of 7.5 cm ones. People do what they want to, but it works.
I have been doing this for years. My own personal “imperial Kosmo” format I have made panels for is 2"x8", 4"x8", etc. It’s close enough to metric Kosmo that I can use metric Kosmo modules alongside my hacked-together imperial Kosmo panels in the same case with no problems.