I think it's a good move to p3d v5, as it will be easy to port most of add-ons and they will be almost all free upgradable.
P3d v5 is much more smooth and provide more fps than v4.5, and v5 and will the plenty off add-ons in a few days/weeks, running smooth. In a few weeks nobody will be using default clouds, people will be able to change sky colors and everybody will be happly deleting the entire v4.5 stuff. And all of this with a small cost: just the new platform price.
I sincerelly do not believe that MS202x will be released so soon and I'm sure that, after released, we will have to: (1) wait to much to be plenty off add-ons and (2) have to pay to upgrade almost all of our current pieces.
Be sure that a entire new platform (like MS202x) is more susceptible to come with bugs and demand more hotfixes/updates/service packs than a new version of P3D.
In a few weeks those who bought v5 will retire v4.5, as almost all stuff will be already ported and with little to zero cost, but the retirement of p3d vX will take place much more time after MS202x arrives.
Don't expect MS202x + all your desired add-ons to arrive in this summer. I think in the next few weeks, many of you who says that is about to "wait for MS202x" will buy v5.
I, personally, am not going to make any kind of plans related to MS202x release. I have in mind that is a full new platform, that hasn't be named MS2020 by it's developer (it's an alias running on the web), being developed by who already aborted another simulator during its evaluation process and that can be released any year from 2020 onwards.