Thanks for all the knowledge dudes! Will def go for a 14 - 17" 16:9 dmd display. Was thinking that it cant be that hard to have a generic video (gat damn flames or lightning bolts probably) behind the dmd on those tables that dont have FullDMD support. 
I think 14" to 15.6" is generally what works scale wise
Many ways to source that.
Personally, i get them from laptops, usually toasted beyond repair laptops whose screen is still good
usually, they are 1366x768 which for a DMD is like way more than enough.
You get the LCD panel model off the back of the LCD and then look for an LCD controller for it, usually about 20 dollars
(also a cheap way to make little spare monitors for stuff)
You can also buy them, at least the 15" ones, they sell them as portable monitors for laptops, they just tend to charge a lot for those
but they work fine
As far as putting filler stuff on it.
Well, Most tables do not use the full screen for the DMD
and the DMD display looks kind of janky if you stretch it to do so, gets really tall and skinny looking
Now pinup i know will play media if you set it up to, i dont know how hard it is as i dont use popper
But a very simple way is via freezy's DMD extensions which you will no doubt be using anyways.
Freezy's allows you to do a lot of custom stuff with the DMD display
And aside from just making the DMD aspect nice, it allows you to do other things as well
This image wont make much sense but, i made it for someone whose cabinet is WB/loony toons themed
You have freezy's apply the image as a DMD frame, and then adjust the DMD to fit in the opening, and the logo fills the rest of the screen
Now one could make all kinds of custom images like this with table logos etc, freey's will let you do a per table kind of thing

These are not full panel, but here are some i made for various tables



here is what some look like in use







There are even some things you can do with non DMD B2S backglasses to make some use of the DMD screen, even if a scoreboard itself is not the proper thing to display
It could be a logo for example


And there are ways to properly add a DMD to most any ROM table that does not have an actual DMD display
Scutters wrote a tutorial on it

So there is a way to do almost anything
Heck i can make an EM table play Budweiser ads from 1961 to 1970 on the DMD screen if you want LOL
None of the above entails any magic from a front end, though i know that they can do it in some fashion or another
the above stuff is just using vpx, vpinmame, freezy's DMD extensions and in some cases flexDMD
Pacman showing a colored DMD where it really does not have one, is flexDMD
this is also flexDMD doing the full screen DMD video, it isnt pinup player, not that pinup is a bad thing
but yea, you can make the DMD screen get used, and it isnt difficult if you are willing to tinker a little
You could have it feature naked dancing Gnomes if you wanted, but i dont wanna know about it LOL