It would be difficult to call people living in Gdansk during Commonwealth to be called Germans or even Prussians. For sure you may claim that them German speaking population was the majority for Gdansk itself (not that much for surrounding villages) but even though they might be called German- speaking "Poles" since Gdansk was defiantly first left German speaking Teutonic Order and further resisted being incorporated by Prussia. For sure however, in 1919 most the local population were Germans.The way that the Polish Corridor was set up in real life likely allowed it to have a Polish-majority population if one considers Kashubians to be Poles. To my knowledge, Danzig was a German-majority city even back in the days of the Polish-Lithuanian Commonwealth.
From the perspective of having "divided" country, it was (as one may see) not uncommon. Prussia before the partition of Poland is obvious example. Now we have Kaliningrad Circuit...
The proposed solution was compromise which could not satisfy neither Germany or Poland. For Poland, the existence of the real harbor was essential to having independence and it was obvious that both for military and commercial reasons Poland will build the new harbor anyway. This however is a economical blow to Gdansk - Gdansk without Poland (as it was clearly seen in XIX century) was degradated to third class harbour in Baltics.
So the only options I can see (assuming no-one wants to have Poland subordinated to Germany after 1919) is:
- grant Gdansk to Poland with part of west bank of Vistula river.
- grant Gdansk to Germany after having it termporarily with certain benefits for Poland until Poland builds its own harbor. This however would require significant subsidizing Poland to have it be able to build it, along with railways. Poland is unhappy in military terms (it is undefendable as in real life) but economically it works. But it costs...