I'm not convinced Floyd Mayweather will finish out his six fight contract with Showtime/CBS, let alone make it to 50. A lot of things could happen like a loss or injury that could potentially derail the plans. But just as an interesting exercise here is a hypothetical path to breaking Rocky Marciano's 49-0 and reaching the mythical 50-0 mark. Assuming he wins all his matches and keeps on keeping on:
44-0 (current record)
45-0 Canelo Alvaraez
46-0 Amir Khan (this supposes that Khan defeats Alexander or bypasses him altogether)
47-0 Lucas Matthysse
48-0 Manny Pacquiao (Paq out of Arum's contract/GBP-TR Cold War ends)
49-0 Keith Thurman
50-0 Adrien Broner
Typing out this list, I really don't see him making it to 50. I only envision a rematch with Canelo if he loses "The One" or it is simply easy work. After this fight, I believe all his remaining bouts will be at welterweight. Khan can be a big money maker and the Canelo fight relieves pressure to take a tough fight. The fight could be Floyd in London although he may not want to give up any kind of advantage, even to Khan. I don't think Mayweather ever underestimates an opponent.
The conspiracy part of me thinks that any kind of official announcement on Khan-Alexander has been delayed until after the Canelo fight because Khan may skip that as GBP pairs him with Mayweather. Maybe even before his traditional May/Sep schedule.
Alternatively, Alexander could fill-in if he defeats Khan or there could be a box-off between Alexander and Matthysse if he wins. Garcia could be a fill-in on this list for Matthysse assuming he wins.
I included Pacquiao for sentimental reasons. I'm well aware that's a (wet) dream. But I think it can happen. Assuming that happens, FMJ may just find an easy fight to make it to 49-0 or just call it a career.
I included Thurman and Broner at the end because I assume at least one of them will become a star by that point and simply because I was running out of legitimate names. I'm not sure he would ever fight Broner actually considering his loose affiliations with TMT.
Who do you guys think could populate this hypothetical list?