Not to disagree with Schwammerl but just to add a couple of points ..
Estonia's market focus has been the US. As an Estonia owner in Europe, Schwammerl is a statistical outlier.

. He has spurned the great makers of Europe to buy into the Estonia / PW cult following.

It's unlikely that hordes of others will folow his lead.

Avid fans of Estonia in the US already own an Estonia grand or are dreaming about one. They're unlikely to sell their grand or their dream in order to get an Estonia vertical. Also, Estonia retailers already have whatever vertical lines they feel fit their business model.
A good part of Shigeru's mystique is in the home visit by a Shigeru-dedicated master tech to fine-tune their piano after purchase. Carrying this practice forward to cover verticals would add costs that would push the price well beyond a K8, a piano that is already expensive. Doing anything less would de-value the brand image.
Schwammerl's "not the biggest of all acoustic piano segments" reference means 'slow moving'. In the current U.S. economy, retailers would be extremely hesitant to take on any maker's pianos that involve high costs to them and turn over very slowly in the showroom. They have enough problems as it is. Pocket markets like Hong Kong and Singapore where verticals make a lot of sense even to high-income shoppers are already well-stocked with verticals from prestigious Euro makers, and the Estonia name is a virtual unknown.
There's a lot of price pressure on any maker's higher line verticals because the cost of a reasonably good grand piano in real dollars keeps getting lower. If this segment generated more sales, Mason & Hamlin would find a way to resume production of its vertical, and Charles Walter would have gone forward with its planned taller vertical.
Ask yourself...if there were a Shigeru or Estonia vertical available for 20k, would you be saving up for it and resisting all the tempting grands that cost less?