I think a traditional roast becomes a different meal if you do too much with the veg - still lovely but just not a roast as PP said.
I've a few ideas, possibly not as 'modern' as you were asking for but different to plain old veg!
Roasting the veg rather than steaming or boiling makes a difference.
We love cauliflower cheese with a roast, you can add any other veg such as carrots & broccoli in the sauce til.
Also leeks baked in a cheese sauce are delicious.
Red cabbage is not just for Christmas! I make a ton of it before Christmas and freeze in family size portions.
You mentioned parsnips - have you tried Delia's Parmesan parsnips?
White cabbage, a little bit of chopped cooked bacon and a splash of double cream all warmed through together is lush.
I prefer mashed swede to cubed. I prefer parsnips roasted to mashed on their own but quite like them in a mixed mash (swede, parsnip, carrot). My Mum used to mash carrots in with potato, which works really well but there would be uproar here if we didn't have roasties on a Sunday.
We had Sunday lunch out recently and I rolled my eyes when they brought it as the veg included asparagus, tender stem broccoli and sugar snap peas - I prefer boring old traditional veg with a roast - but actually I was proved wrong and made me realise I need to be more adventurous too, so watching this thread with interest. .