Here's an idea for a Frontier/Data Squad Crossover.
After the events in frontier (how long is your choice) takuya has to go live with his cousin marcus damon for a while (circumstances are up to you). While there, takuya learns of Marcus' involvement with DATS (already joined before takuya got there but before Keenan comes to human world). Following learning about digimon appearing in the real world, takuya gets his d-tector back in order to help maintain balance between human and digital worlds. Takuya and any other legendary warrior, DO NOT get a digimon partner, but once again receives the spirits. The only person who HAS to join him is Tommy, the rest are optional. All legendary warriors that appear must unlock their fusion forms. Tommy must strike up a strong friendship with Keenan and help him and falcomon adjust to the human world. The digimon MUST know about the legend of the legendary warriors and the events that took place in frontier, even if its an ancient legend to them. MUST make it so ANY legendary warrior that appears can unify spirit evolution (I love emperorgreymon and magnagarurrumon but it leave the others as useless. Let them unify spirit evolve once in a while) Also, takuya and tommy (and whoever else joins them) MUST become Susanoomon at some point. If only Takuya and Tommy appear, the rest of the spirits are stored in their d-tectors. Takuya and Tommy will be much more sympathetic to the digimon quicker than DATS.
That's all for this one! Please let me know if you take up the challenge! Also, PLEASE try not to abandon it.