Boxed Sets

Two, three or at most four omnibus volumes might be packaged as a boxed set. I envisage:

Two-Volume Sets
Heinlein's Future History
Anderson's Psychotechnic History
Anderson's Time Patrol Series

Three-Volume Sets
Doyle's Holmes
Fleming's Bond
Anderson's Technic History Vols I-III

Four-Volume Sets
Blish's Major Works
Anderson's Technic History Vols IV-VII

James Blish's major works, each to be collected in one volume, are Cities In Flight, The Seedling Stars, the "Haertel Scholium" and After Such Knowledge.

This would be a convenient way to contemplate several comparable or connected works. The Bond series is structurally similar to the Holmes series which connects with the Time Patrol.

History is a major feature of these works. Every novel is set in a particular period. Bond is becoming as dated as Holmes. In the works listed here, Heinlein, Anderson and Blish present fictitious histories. Additionally, Anderson presents historical science fiction in the Time Patrol series and Blish presents historical fiction in Volume I of After Such Knowledge. Both Anderson and Blish wrote historical fiction. Blish's output is much smaller than Anderson's but his single historical novel, Doctor Mirabilis, focuses on Roger Bacon, the founder of scientific method, and thus is a conceptual prequel to Frankenstein, the first science fiction novel.

Other works are also relevant. CS Lewis' Ransom Trilogy is a partial precursor of After Such Knowledge and indeed could be collected in one volume with a few shorter works by Lewis: see here. Before Lewis and Blish were the major works of Stapledon and Wells which do not lend themselves as easily to omnibus collection although there was a one-volume edition of Stapledon's two Last Men novels.