Personally I would love if they included one page which lists -all- currently (commonly) available units and variants of a specific faction in the era in question.
I know there is the Master Unit List. The overview you get by having your new toys and old stand-bys in one book/PDF would still be appreciated. But maybe that´s just me.
One page?? The MUL BV PDF was one era, and 208 pages. let's say we formatted it to cut out two-thirds of the text, that's still 70 pages.
And would be immediatley out of date as soon as a new publication came out with additional information.
Meanwhile, the planned series listing production for each era, nobody (in significant enough numbers) cared enough to actually buy it.
So you get it for free, on the MUL website, instead. And Layout, Development and whoever else would be involved in a print/PDF release can concentrate on stuff that people actually want to pay for.