Under the current round, if a gTLD registry wants to release 2-letter country codes (ISO- 3166) at the second level, it can a) propose it directly to the related government and ccTLD manager, https://www.thedomains.com/2017/03/...wo-character-domain-names-new-gtld-namespace/ if ever comes to be..are we going to see the return of sub domains being sold e.g. {some-string}.uk.shop
No. CentralNic already does this. They are shutting down GB.com soon I think, or already did? Seems GD bought the 2-letter domains from CentralNic. http://adamyamada.com/who-bought-centralnic-domains-godaddy/ It's caused problems for registrants when the company lost control of domains. EU.org, ZA.net, and ZA.org are free services.
I owned uk.guide and received very little interest in its resale. I really can't see a market for sub domains as there is already resistance to new gTLDs.