The thing is that DCS have several time eras and each time era have it's audience. It is the WW2 era with the spitfire, mosquito. BF-109 etc. Then there is the cold war era ranging all the way from 1950 to 1990 with the Sabre, mig-19 and the Tomcat. Then lastly there is the post-cold war era where we see the F-16, JF-17 and the F-18 etc. There is overlap between the eras but you get the point.
All up until the release of the F-14 all we had was essentially the mig-21 and F-5. Not exactly the most sought after cold war jets. However the F-4 (together with the mig-21) is like the most iconic cold war planes. A cold war without the F-4 is like a WW2 community without the P-51. With the release of the F-4 and mirage F-1, the cold war community will get a massive lift as it recives two of it's most iconic jets. Furthermore the F-4 will also add alot to the Persian gulf map in particular as it opens up a floodgate of missions especially Iran-iraq war scenarios but also all up into present era as Iran still fly them.
ED decided to postpone the development of the F-4 back in 2018 to instead focus on the F-18 and F-16, which was a wise business decision as it did draw a <profanity>load of more people into DCS.
But it will be interesting to see the sales numbers for the F-4E compared to other modules, I suspect it will be on par with the F-14. And ofc it helps that it is made by the most trusted third party developer.