I train xc ski in the winter and cycling in the summer. I use TR year round with two seasons and I use TR plans for each (with different plans based on event/personal goals). Basic training concepts are the same.
My comment is more about being serious with ski workouts as part of a training plan, less so about having fun mixing it up.
In terms of ski workout instead of a cycling one, the biggest difference is that your effort is split across your whole body and less focused on legs. Therefore, a ski workout won’t load your legs like a cycling workout does. If you adjust for this, then you’ll be fine.
Another way to consider this is to know your legs will be fresher than the same workout done cycling but that you’ve still done the workout TSS. If you need, use a free TP account and get a nordic ski HR TSS (maybe Garmin Connect does this, I’m unsure).
Watch your HR as you can easily push your intensity up with nordic ski, especially when new and have beginner technique. In this regard, classic can be easier to adjust your effort from easy ‘ski walking’ to full on ‘hill running’.
That said, I’d suggest skate technique is more cycling specific.
Otherwise, a big plus for me is the mental stimulation of two sports. And to mix it up the other way, rollerski sessions are fun in summer too.