Yeah definitely. They're almost impossible to find unless you actively go looking for them and knowing that a big game is coming up would likely generate interest in the game/ladder. Maybe in the same way you have a promo challenge bar you could have an active official challenge bar (visible only when there are active challenges or maybe for a short time after like Jedi suggested). Heres a real basic example of the front page (ignore the awful spacing):
DESCENT CHAMPIONS LADDER
STANDINGS.....REPORT.....HELP.....FORUM.....HISTORY
Standings.....Recent Matches.....Award Holders.....Compare Pilots.....War Journal
Active Challenges!.....(left click to unfold)
Challenger.....Opponent.....Day(s) left.....Score.....Comment (from challenger)
Jediluke........Morf.............Complete....20-2.......Water them!
b2af.............Sirius...........Expired.......blank......any map lets rumble
Lee..............moh.............2................blank....FRIEND REQUEST SUBMITTED!
Bronze Tier......Morf.............13..............blank......It was inevitable. The clocks a ticking

Jediluke
Mark392
Diablo
Vainiac
etc etc