From what I can tell, the .in registry would most likely use the .in extension for IDNs before the co.in. Does this mean that the .in extension will most likely be the dominant extension over the long run?

What do you guys think about IDN.in vs. IDN.co.in ?

It makes sense.

.in is much easier for non-English speakers to remember.

Whether that means the registry now favors .in is a different matter but definitely possible

.co.in is also easier for non-english speakers..

.in and .co.in are new extensions. see .co.uk are now become very popular extensions.

how the nonenglish speakers remember the .co.uk? like that

In near future .co.in will reach non-english speakers too..

Its not the case, there is a basic reason why .co.uk is so much popular. because they don't have a .uk extension, so they just have .co.uk , whereas for india we have both, and hence .in would be more popular than .co.in

I never go with a double dot TLD. Anyhow, I have seen most of the big Indian organizations like Colgate and many other known organizations are using .co.in as their TLD. So, I suppose .co.in is what Indian woulds would be more comfortable with, than '.in'

So, I would go with .co.in