we are working on 3 releases simultaneously - 7.4.1, 7.5.0 and neXt, all are progressing -we do all our work out in public so you can always check the state of a release (click the Commits tab to see recent commits)

https://github.com/dnnsoftware/Dnn.Platform -this is the 7.4.1 code

https://github.com/dnnsoftware/Dnn.Platform/tree/feature/7.5.0 -this is the 7.5.0 code

We do all our changes via pull requests, so you can see what's coming https://github.com/dnnsoftware/Dnn.Platform/pulls (the top 2 items are additional updates for MVC support in 7.5.0)

When we release the first CTP, there will be some documentation/blogs coming out, as we want people to try the new bits and give us feedback , however there's plenty of good stuff there in the code already e.g. here is the MVC based HTML module (still needs a little polish, but it shows everything working)

https://github.com/dnnsoftware/Dnn.Platform/tree/feature/7.5.0/DNN%20Platform/MVC%20Modules/Dnn.Modules.Html

As to the difference in 7.5.0 and 8.0.0, we wont have an exact answer until Microsoft have a final version of asp.net 5.0 - we know there will be breaking changes, but we believe that it will be minor (such as changes a few class inheritance references) . It's more than likely that a simple utility will be created to automate any minor breaking changes.

https://dnntracker.atlassian.net/secure/RapidBoard.jspa?projectKey=DNN&rapidView=52 is our kanban board of what we are considering .This covers 7.4.1/7.5.0/neXt issues, you can see individual releases by clicking the "releases" icon e.g.  https://dnntracker.atlassian.net/projects/DNN/versions/13801 is 7.5.0. Please note, we use 2 weeks "sprints", so you often only see the next two weeks worth or tasks, with a few for future enhancements defined in the backlog (we will estimate how long they take and assign them to a relevant sprint as we finish other work , but you can see the "story" items at https://dnntracker.atlassian.net/issues/?jql=project%20%3D%20DNN%20AND%20issuetype%20%3D%20Story%20AND%20resolution%20%3D%20Unresolved%20AND%20fixVersion%20%3D%207.5.0%20ORDER%20BY%20priority%20DESC%2C%20updated%20DESC )

That said, 7.5.0 is primarily worked on by DNN Corp staff, at least until the CTP after which we hope to get pull requests.

If you're interested in contributing, the best way is to read http://www.dnnsoftware.com/wiki/page/github and get a start by tackling some of the hundreds of logged, unfixed bugs (just do a search for unresolved, unassigned platform bugs)