DS Note is just one example, there's buttloads of software that Synology cranks out for these little boxes, including security cam software. Problem is, tracking down which camera works with the NAS is non-trivial, and frankly more trouble than I care to expend. Now if Synology said, "here's a $200 camera. Point it at your NAS. All data stays on your local network, no 'cloud' services to rely on. Sorted.", I'd buy four of them that same day, no questions asked, shut up and take my money.
IOW, yes, there is a currently available solution. What there isn't, AFAICT, is a "click here, wait two days for Amazon, have it running five minutes after you open the box" like Nest or Withings.