For a few years now, Delphi has had support for the Windows Dektop Bridge. This is a Microsoft technology allowing to create UWP (Universal Windows Platform) applications based on a traditional Win32/Win64 application. Delphi IDE simplifies this process (making it smoother than with Microsoft own tools) as you ca read in the docwiki. While there are still some hurdles to enable desktop bridge apps in the store (there is an manual authorization process from Microsoft) the cost to be on the store is fairly low.
Over the last year Microsoft has been increasingly pushing developers towards the Windows Store (actually, now called Microsoft Store) for applications distribution on Windows — where it competes mostly with game distribution platforms. They even released a version of the operating system, Windows 10 S, which only allows installation of apps from the store. However, this has seen a limited traction.
In terms of costs, the Microsoft Store has long offered a 85% revenue share, which is generous compared to the mobile counterparts (at 70% in general). They were offering some special rates from links to the developer site. Now they have rolled out a new and simplified revenue sharing plan. In short, for anyone who buys through an external link (that is, not browsing or searching in the store application itself) the revenue share will be at 95%. This is lower than the processing, invoicing, and payment commission costs of a direct sale — plus you have to pay for the infrastructure and more, handle updates process, and so forth.
If you sell Windows applications to the public (consumers, but also companies) I suggest you to double check the Microsoft Store distribution model, given how easy we have made turning your existing VCL and FMX apps into store apps and how generous the revenue share from Microsoft has become.