Duo prop outboards?
 

Suzuki had (and maybe Yamaha as well) one of these at least 10-15 years ago , but of course the engines were a lot smaller then .
Two of the guys on the Donzi.net have them on their C16s and wouldn't trade 'em for anything .

Now ,now , no need for embarrassment ! lol
Actually if I recall , going back a few decades , Yamaha also produced a jet drive outboard for a short while .
If you haven't already , the next time you see someone with a smallish single engined D/P boat ask them if you can go out for a test.
I know that most people think they're miles slower than a single prop but they're really pretty amazing .

Actually I didn't know that there was still D/P outboards available so seeing those monsters was a real education . I think the previous Suzuki model I was thinking of was about a 150hp.

For some reason I'm thinking that if there was anywhere in the world where one could get a glimpse of a jet outboard it would be in your neck of the woods . I think the Yamaha models were around 115-125 hp , hmmm , maybe a 90hp ?

~Note to self......
See something new, Google it first then post later if in doubt. ~

In most instances it's still better coming here first !

supposedly mercury has a twin prop lower in development

Yamaha outboards has twin props out for years. Volvo Penta was the first for the sterndrive market.

Also Yamaha Outboards had a Catalyst emission controlled outboard out since 2001 - It is not sold in the USA not sure where it is sold but was made way back then.

Yamaha still makes a sterndrive twin prop outdrive as well. They have been done with I/Os since 1993 in the USA market but those where single prop apps up to 300 hp all carb apps - 1988 thru 1993 USA.