As we know, the German Bundestag uses a mixed-member proportional (MMP) electoral system, with constituency votes that are majoritarian (299 seats) and party votes that are proportional (299 seats), plus the overhang and leveling seats.
What is the maximum number of seats there could theoretically be in the Bundestag?
Suppose CDU gets 100% of the vote in all constituency elections, and the SPD gets 100% of the vote in party votes. Or suppose that CDU wins all constituency elections with only 1% of the vote in each district, but all other parties got less than 1%. (I know that Germany has introduced a 5% threshold, but let's suppose there is no threshold.)
My impression is that the overhang seats would include as many as the seats that the number of constituency votes that need to be compensated (598+299=897). In this sense, the "proportionality" of the system counts the district majorities in tandem with the party proportion (i.e., 1/3 of seats are allocated to plurality of 1/3 of votes, and 2/3 of seats are given to the other 2/3 of votes).
Or is there no upper limit to the size of the Bundestag? In theory, if the parliament needs to have the same distribution as the proportion of party votes, then there could be an indefinite number of overhang votes.