It may be a bit of a hybrid.
There are portions of the New POS software that act with lightning speed. For example, the initial login screen where you type in your TM number. That's probably the fastest response to touch I've ever seen on a Target device, ever!
Once the application is logged in is where the nightmare begins. I think this Positron software or whatever is a shell running on the RAM of the Windows PC, but the loaded graphics and overall "POS" may be web parts.
The idea of New POS also includes the ability to deploy it to anything and everything. If it's purely web-based, you'll run into rendering issues as browsers across different devices (even if the same browser — think how differently your Chrome browser handles pages on a computer than your phone, even if you have either set to display it as web/desktop version) and it'll ruin the goal of "one size fits all" deployment.
If you have a chance, play around with the myCheckout app on the myDevices with the Verifone attachment. That's basically a miniature version of New POS when you put it in Line Busting mode.
Here's also a current "can you suspend/pick up" relationship between these rollouts.
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