I have read SQL21 is on the cards, when would is the release?
There is no public information on if and or when the next major release of SQL server will occur.
Benefits from Upgrades from sql19 to sql21 > im looking for speed and paralism fixes?
Since the product has not been officially announced, there is no information for this.
Do i wait for patch to be released before upgrading?
This is your personal preference. You should be patching to the latest versions, always.
Different in lsence cost from sql2014 enterprise to sql21 enterprise?
Again, since there is no public information there may or may not be a change in licensing for vNext.
-Sean