The date picker doesn't appear to permit keyboard input and tabbing out of the field is restricted? That would be a contravention of accessibility guidelines?
This is a great suggestion and call to awareness. To get more visibility from the development team, could you add a feature request in the K2 Five product feedback page on the uservoice site? Accessibility is extremely important, so if you have more ideas on how the product can be improved in this area, you can let the dev team know on that page. From there they can tie the ideas in to a development sprint and capture requirements better too.
K2 Five: Hot (496 ideas) – Customer Feedback for Nintex (uservoice.com)