BMD have multiple hardware options for playout, one doesn't even require any software.
HyperDeck Studio Mini - can provide video overlay with key and fill (yes, you still have to create the video but they have the software for that already, Fusion)
Decklink cards (4K models have internal key to overlay graphics on live video for post Atem mixing, duo 2 and Quad 2 can provide key and fill signal to Atem, Use CasparCG open source software for real-time updatable templates using Flash or HTML technology, lots of other 3rd party software that supports this hardware).
UltraStudio HD Mini (Thunderbolt 3 device that produces key/file signal for ATEM keying, still needs software like CasparCG).
For video playout there is an excellent, and free, CasparCG client
http://cim.works/producten/playout-xpress/#downloadI have also use FFPlay.exe to play out video using a DeckLink card for videos.
If I was a better developer I would add DeckLink support to OpenLP...