This is a altered timeline of what would happened if digimon overtake pokemon's popularity:
February 27, 1996 - nintendo and game freak staff had noticed many bugs (missingno. and other glitches) in Pokemon red and green. the game was delayed until further notice.
April 1, 1997 - Anime was also delayed as well as mangas based on pokemon were cancelled until further notice.
June 26, 1997 - Meanwhile, Digimon was released in Japan but however as Bandai's main Successful franchise.
March 28, 1998 - During production, Pokemon anime tries to cash in on what made Digimon so popular, leading to more similarities.
April 18, 1998 - Digimon is now released in US.
March 7, 1999 - The games and anime are released in Japan later than OTL. Seeing that the Pokemon games are successful, Digimon's creators feel threatened over their multimillion market and sue Nintendo for plagiarism, especially for the content of the anime. While trial is ongoing, it gets attention of public (c.f. the Apple vs. Samsung trials) and they come to see Pokemon as being the rip-off.
April 2, 2000 - Nintendo of America now has to decide what to do with the Pokemon intellectual property. It would be a massive risk to market and release the franchise as-is in the USA, since a similar public controversy would result and Digimon would try to block them from this market too (the Japanese verdict hasn't been decided yet so it's uncertain what would happen). They decide to rename and edit the whole thing to heck and back (c.f. Macross and Robotech) to remove any similarities. Unfortunately, in their rush they completely overdesign-ized it.
May 18, 2000 - The alt-Pokemon is released in USA and gets awful reviews. The franchise bombs.
June 26, 2000 - Digimon's lawsuit is unsuccessful but the damage is done, the public now see Pokemon as dishonest and plagiarised.
January 1, 2001 - The negative reputation in Japan and the heavy financial losses in USA leads Pokemon to falter as a franchise. It still exists but it never attains the glory that it did OTL. Meanwhile, Digimon sweeps up the market. Now, Pokemon is to Digimon as OTL Duel Masters is to OTL Yu-Gi-Oh.
More timeline to soon!