After I saw the improvements of the email client in suite I decided to give it another go.
Downloaded 7.8 RC1
Running Plesk on Ubuntu, PHP 7.0 with Apache FPM (NGINX proxy)
Install gave setup screen, but console was was telling me that there were several CSS and even JS files missing. Could not finish the setup because it kept telling me that the Yahoo setup was mandatory even I have filled in and selected the "other’ settings.
So no way to continue the install and I installed the stable version, then upgraded to the latest RC1 and at least I had a working CRM
Home page works fine, most modules seems ok.
I added two email accounts but only see them in the home screen dashlet. My mail client screen remains almost blank:
No results found for “basic_search”
Create “basic_search” as a new Email
Are the two only lines there.
So I can create a new mail but not see mailboxes. Console give me about 18 JSerrors.
Went back to PHP 5.6 to check if that helped but nope no diff.
Also when opening a mail via the dashlet all HTML becomes plain txt.
Bit disappointing I must say. Of course it is not a stable release but with a final release around the corner this all seems a bit problematic.
I have run almost all repairs (nice option it seems) but the diagnostic file shows a bit too much details to upload here.
There are way too many issues to post them all here and my time is limited.
On the positive site I am pleasantly surprised about this CRM, got the Magento sync working with an old SugarCRM extension and like the look and feel. Hope this was a one off but now it looks too much like my vTiger times 
Anybody recognizing a basic issue that could solve the issues? Is there a github dev version?