Come to Rhein-Main! Lots to explore beerwise but also nature and sightseeingwise. I will happily show you around and provide info.
Base yourself in Mainz (we have 4 breweries) and do daytrips to Frankfurt (dive into applewine if you are interested), Darmstadt (3 breweries), Rüsselsheim (2 breweries), Worms (2 breweries), Rheingau (if you are into wine) and even further daytrips are easily possible by train to: Koblenz (two breweries on the way there already with train stops), Mannheim/Heidelberg. And way more breweries to see off the bigger cities but easy connections by trains.
This is also one of the ideas I have, actually. Stay in Mainz/Frankfurt a couple of days and then go all the way south from Darmstadt to Mannheim using the Regiobahn (with stops in Auerbach/Bensheim, Heppenheim, Weinheim).
I know that’s more of a wine area, but looks like each small town has at least one hausbrauerei with restaurant and the pictures of those town are so inviting!
There’s actually a lot when looking into the agglomeration areas. Imho options are:
Route Frankfurt - Darmstadt - Heidelberg
Halle/Saale + Leipzig
Hannover + Goslar
Erfurt + Weimar + Jena
Freiburg as start point for black forest?
If you prefer traditional German beer styles, you might want to consider the much neglected Oberpfalz and Niederbayern beer regions. You could stay at Regensburg (8 breweries and a fascinating medieval centre which somehow survived WW II) and plan daytrips by train to Straubing (3 breweries) and Passau (4 breweries), Kelheim and the Altmühl valley, or nearby Hallertau hop growing area with many cultural highlights and lots of traditional breweries–in fact, this region rivals Franconia for brewery density. There is a very helpful guide which covers every brewery in the area: Harald Schieder, Ralph Forster: Bierführer Ostbayern (published in 2014 but still not too much out of date).
My next trip to Germany (most likely 2021) is a long drive from Calais to the coast of Mecklenburg-Vorpommern, via Bremen and Schwerin. Hopefully staying in brewpubs when possible.
I have done similar road trips to Berlin, the Mosel and Dresden/Czech Republic. I need to review places in both Bremen and M-V for the full set of Bundeslander. In fact my wife and I should be in Cochem as I write this.
Regensburg und die Oberpfalz, immer eine Reise wert…
Genauso interessant eine Reise von Dresden in Richtung Prag ( wenn die Grenzen geöffnet werden). Mittlerweile gibt es in fast jeder tschechischen Stadt eine oder mehrere Mikrobrauereien, gar nicht zu reden von den ca. 50 (!) Brauereien in Prag.