If WotC's plan is to design it similar to the 5e DMG, then I'd prefer if essential things like magic items would also be available in a smaller/lower cost companion. IMO too much of what was in the DMG was novice and introductory and I have other publications that are reasonably system agnostic (i.e. PF1E GameMastery Guide) that do a better job covering it. While I made use of magic items, crafting, sub races, sub class and monster creation info in the 5e DMG, everything else was just filler. I needed it for encounter creation guidelines in the early days of 5e, but WotC eventually released the free 5e DMG PDF which included that. Not to mention others eventually published alternatives.
These days I much prefer PDFs to Hardcovers though, so I'm unlikely to migrate to OneD&D anyways.