Sounds good to me. It seems like it would make a thicker, less watery ketchup, which I prefer. But I love pureed butternut squash (I've been know to eat a bowl of it for lunch) so I'm not apt to have enough left around to try it.  I have added squash puree to chili to thicken it and that worked well.  Oh, and I've also added it to beef stew.

Another idea is to make squash butter. No, I haven't tried it, but I make spiced pumpkin butter and it's lovely. And easy. Squash puree should work just as well, I would think. You use it like you would apple butter.  Most people eat it on toast or pancakes or oatmeal, but I like it on cottage cheese.

Have you made squash fries?  You can make them in the oven the same way you do baked sweet potato fries: just cut the squash into french fry shaped strips, toss it with oil and your choice of seasonings, and bake in a single layer on a baking sheet.  One recipe I've seen, but won't try until the weather cools down, is to season them with curry and cinnamon and serve them with chutney as a dipping sauce.  Oooh, I'm making myself hungry.

I also like quinoa mixed with diced butternut, zucchini, and onions (but I confess I buy the butternut pre-diced).

Just some random ideas for using extra butternut.

They sell pre-diced squash here in California, anyway. You can find it both fresh and frozen. Sometimes it takes some muscle to cut and peel squash when it's raw, so I find the pre-diced kind a convenience.