It doesn't sound so far-fetched with the advancements brought forth by the 4680 cells.

With the reveal of Tesla's new 4680 battery cells and the announcement by Elon Musk that the Model Y built in Germany will eventually receive those cells, a 400-pmus ile version of the Model Y seems completely doable now.

According to Musk, the European-built Model Y will use the 4680 cells. It will also feature the structural battery pack, the mega castings for the front and rear parts of the body, and also the innovative paint process Geico Taikisha offers.

This means that the German Model Y will be the most advanced around. However, as Musk explained, at a later point in time both Fremont and Giga Shanghai will produce this advanced variant of the Model Y too.

Equipped with those 4680 battery cells, the Model Y could in theory go much further, provided it has a battery pack that's of the same capacity of the current Tesla Model Y Long Range AWD version.

At Tesla Battery Day, Musk revealed that the 4680 cells, combined with the structural battery pack setup, could increase the range of the vehicle by some 30%. Currently, the Model Y Long Range AWD is rated at 316 miles. if you add 30% of additional range to that figure then the result is an astonishing 410 miles of range. 

So, will we see a 400-plus mile Model Y? We might. Or perhaps Tesla will employ the 4680 cells in a battery pack of lower total capacity so as to not outdo the range rating of the Tesla Model S, which currently sits at a high of 402 miles.

YouTuber Bearded Tesla Guy adds some additional information on the possible 400-plus mile Model Y, stating:

Giga Berlin will be utilized to support the Tesla Model Y demand for the European market once complete. This is already widely known at this point. What was not known, until Elon Musk took to Twitter this afternoon, is that the Tesla Model Y in Giga Berlin will come with the 4680 integrated battery cells as well as the solid cast front and rear assemblies.

The Battery cell alone is expected to increase range by 16% and reduce cost of the battery pack by an additional 14%. The single casted front and rear is expected to increase range another 14% while reducing cost of those components by 7%. All in, if the battery pack size is the same, 75 kWh, then we would expect the EU Tesla Model Y to come in at 30% more range than the current N.A. Tesla Model Y LR AWD.

Of course, this is all speculative at this point in time in regards to the range rating of the Model Y equipped with 4680 structural battery cells and single casted front and rear sections, but provide Tesla sticks to 75 kWh and that the percent improvement claims provided by Tesla are accurate, then over 400 miles is possible.

Gallery: Tesla Battery Day 2020