Photos please.

I don't think a downdraft would have the power for a 30 inch let alone a 48. who is redesigning your kitchen?

Wow, tough call. I absolutely hate cook tops in the island but in front of a window....what a mess!

You can only put a cooktop in front of a window if that window is not operable. It's a fire hazard and will not meet code in most places. I've done pop-up downdraft vents in an island before. It works fine as long as you're not doing a ton of frying. Wolf and Thermador both make good options.

I had a gas stovetop with a downdraft on as island, and I thought it was great. My island was large enough to still have a wide area behind the stove for countertop use. I liked that the vent was unnoticeable most of the time with a clear view outdoors. I cooked dinner almost daily, and it worked perfectly fine for the infrequent times I needed the vent. I also had a large window and French doors that were often open nearby. I think a a lot has to do with your particular space, and what types of things you cook. Mine was a downdraft for 4 large burners plus a center griddle.

No stove or vent by the window. A sink should be by the window.

Photos and floor plan (to scale on graph paper) would get you more help.

Get a better Kitchen Designer. If you can afford the too large for a normal suburban kitchen 48” range, you can afford the better kitchen that surrounds it. Don’t shove something like that into an awkward bad layout. Which any layout like you’ve proposed IS. It’s bad. Do better. Hire a real Kitchen Designer to start.

Years ago I had a JenAir range. The downdraft didn't do much. They we did a tall telescope downdraft, big improvement. Now I have an over the range hood bigger improvement.