I think the XFL will be successful. Vince McMahon knows marketing and has the finances to make it work. Yes I know it failed 20 years ago but I think the 2020 XFL has big advantages over the previous version in 1999 XFL and advantages over the AAF.
The 2020 XFL already has deals to air on ABC, Fox and ESPN. Obviously all of those companies will also advertise/promote the new league. Those companies never even set up a way to see scores of AAF games on their websites, and certainly didn't advertise/promote the league on television. 1999 XFL aired on only on NBC and the AAF aired on the NFL Network and CBS Sports Network. ABC, FOX and ESPN didn't want the AAF to be successful.
AAF ratings were actually pretty good, consistently beating NBA ratings in head-to-head broadcasts, despite only being available on an obscure TV station or on-line at the NFL Network. AAF simply ran out of money.
2000 XFL also does not have age restrictions or restrictions on leaving for the NFL, (the AAF required 3-year contracts) so a college player could go pro and play for the XFL at any time then enter the NFL draft. Its not even clear if you have to play in college to go into the XFL. If that's the case there are plenty great high school athletes that simply don't play in college because of academics.
Salaries are supposed to be much more than the Canadian football league up to $300,000 for the top players(starting at $7,000 per game), so it may steal some players from Canada. The AAF paid 250,000 for non-guaranteed 3-year deals. (less than 85,000 per year)
Also Gambling. Vince McMahon is a partial owner of Draftkings, so my bet is that gambling will be directly incorporated into the 2020 XFL in some way.