I was thinking on those lines also--one disc per decade, and I'd make sure each one clocked in near 75 minutes each.
The only thing I'd stall on is anything newer than the early 90s. Janet Jackson's Rhythm Nation is probably one of the few I have from that era. 2002 and onward? I'd have to leave that disc blank as I probably know nothing about any of the music made during that era.
I'm pretty much in the same boat...in fact, I'm fairly challenged as far as who was on what label from the 80s on.
But here's a revised beginning of a 5-disc set, 75 minutes (give or take) per disc, what I'd do if they asked me, without worrying about licensing deals and trying to give some depth and texture to the compiltation.
I'll let other (probably younger) people do the newer stuff:
Disc 1 (1962-1971)
1. Herb Alpert & The Tijuana Brass: The Lonely Bull
2. Julius Wechter & The Baja Marimba Band: Comin' In The Back Door
3. We Five: You Were On My Mind
4. Sandpipers: Guantanamera
5. Claudine Longet: Meditation
6. Chris Montez: The More I See You
7. Parade: Sunshine Girl
8. Merry-Go-Round: You're A Very Lovely Woman
9. Jimmie Rodgers: Child Of Clay
10.Procol Harum: A Whiter Shade Of Pale
11.Wes Montgomery: Windy
12.Tommy Boyce & Bobby Hart: I Wonder What She's Doing Tonight
13.Antonio Carlos Jobim: Wave
14.Sergio Mendes & Brasil '66: The Look Of Love
15.Phil Ochs: Pleasures of the Harbor
16.Herb Alpert: This Guy's In Love With You
17.Shango: Day After Day
18.B.J. Thomas: Raindrops Keep Fallin' On My Head
19.Milton Nascimento: Bridges
20.Sonny Charles & Checkmates, Ltd.: Black Pearl
21.George Benson: Tell It Like It Is
22.Joe Cocker: The Letter
23.Carpenters: (They Long To Be) Close To You
24.Free: All Right Now
25:Cat Stevens: Wild World
26.Lee Michaels: Do You Know What I Mean
Disc 2 (1972-1981)
1. Humble Pie: Hot N' Nasty
2. Michael Murphey: Geronimo's Cadillac
3. Stealer's Wheel: Stuck In The Middle With You
4. Billy Preston: Will It Go Round In Circles
5. Sister Janet Mead: The Lord's Prayer
6. Paul Williams: That's What Friends Are For
7. Joe Cocker: You Are So Beautiful
8. Captain & Tenille: Love Will Keep Us Together
9.Ozark Mountain Daredevils: Jackie Blue
10.Nazareth: Love Hurts
11.Joan Baez: Diamonds and Rust
12.Brothers Johnson: I'll Be Good To You
13.Tubes: Don't Touch Me There
14.Peter Frampton: Show Me The Way
15.Barry DeVorzon & Perry Botkin, Jr.: Nadia's Theme
16.Rita Coolidge: Higher and Higher
17.Pablo Cruise: Whatcha Gonna Do
18.L.T.D.: Back In Love Again
19.Chuck Mangione: Feels So Good
20. Joan Armatrading: Show Some Emotion
21. Supertramp: The Logical Song
22. Herb Alpert: Rise
23. Styx: Babe
24. Ali Thompson: Take A Little Rhythm
25. Lani Hall (f/Herb Alpert): Come What May
Disc 3 (1982-1991)
1. 38 Special: Caught Up In You
2. Human League: Don't You Want Me
3. Joe Jackson: Steppin' Out
4. Police: Every Breath You Take
5. UB40: Red Red Wine
6. Bryan Adams: Heaven
7. Simple Minds: Don't You (Forget About Me)
8. OMD: If You Leave
9. Sting: If You Love Somebody Set Them Free
10.Falco: Rock Me Amadeus
11.Jeffrey Osborne: You Should Be Mine (Woo Woo Song)
11.Janet Jackson: When I Think Of You
12.Breathe: Hands To Heaven
13.Chris DeBurgh: Lady In Red
14.Suzanne Vega: Luka
15.John Hiatt: Slow Turning
16.Amy Grant: Baby Baby
17.Extreme: More Than Words
(and to be honest, this is where I run out of gas. Someone else needs to flesh out the remainder of disc 3 and take disc 4 and 5).