Is a baby stroller "furniture" ?  

I say who cares if modern...
I say who cares if modern babies are facing forward. They have all their entire lives ahead of them to learn how to talk back to and laugh at their parents.

I'm thinking some Scientists have...
...nothing better to research. I'm keeping an open-mind, but doubt this is one of the reasons language has gone down hill. It could be a multitude of things; this one doesn't really empress me.

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That's a disappointing reaction, I guess. Did you read the whole piece ? Possible language acquisition wasn't the only benefit noted; babies were happier when they could see and interact with their parent/caregiver.
Perhaps we don't have parents here. I'm not one myself, for the record.

Are forward facing strollers something new?
Baby carriages face the adult, but haven't strollers always faced "forward"?
Of course, if strollers WERE redesigned to face the parent, something tells me that researchers would then warn us that backward-facing strollers have a negative effect on babies' visual & social development.

A friend of mine has a 4 year...
A friend of mine has a 4 year old. Both parents spend considerable time with her, including talking and sign language. I've notice her socials and language skills are above average. A friend of the family has a daughter that had been diagnosed with a mild form of Cerebral Palsy, which was proved wrong I believe and don't recall the details. Anyway, her language skills were slow in developing or not talking at all. The Doctor essentially prescribed sign-language. It works! No a cure-all, but certainly contributed. She speaks with ease now.
What am I getting at? As the researches in the article pointed out, early neurological development is essential. It make sense to me, that the more personal interactions in those crucial early years, the greater social and language skills develop. As you pointed out SDR...the children were happier and laughed more.
Just speaking about children newborn to age 3...Could it be that front facing strollers are a sensory overload for children? In turn creating a jumble of information difficult to process. Children facing parents are able to focus on just the parent or mild peripheral influences and easier to assimilate new things with less stress, and thus happier?

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I have heard more than once that children respond well to consistent guidance and input. It may be that a caregiver's persistent interaction with the infant and child is preferable to the random greetings of friends, neighbors and strangers -- though I'm sure those are desirable as well ! The newly-reported research seems to reinforce that view.
Science operates when researchers make observations, report their findings, and try to make sense of the information. Entertainment or popular appeal aren't the point.
On the streets where I live, rear-facing and forward-facing strollers are seen in roughly equal numbers, I would say.

Sorry to disappoint. It's an...
Sorry to disappoint. It's an interesting article, SDR, and now that I have read it twice, it is still an interesting article. As a sociology major, it was driven into me quite some years ago that some things can be analyzed to a point of excruciating conjecture, for minor good purpose, especially where childhood development is concerned, so I admit to a certain prejudice here and lack of appropriate stroller spirit.
That said, the potential correlate presented in the link was, at least to me, simply not terribly convincing. But I imagine there are articles being written on strollers as we speak, and I think it may be very possible an academic journal devoted exclusively to this exact subject could be found down at the campus library.

furniture - industrial design
I don't know if it is a furniture, but indeed a very industrial design product interesting to design and analyze.
There are lots of clever designs.
When babies are smaller, months, up to 1 years: in front to parents. When they have months is important to watch them all the time.
Later they are so excited with the external world... There are other human being in the world...! not just mom and dad!. Dogs, birds, trees,
colours. But is true that later again, they want to comment all those new discoveries.
""Let's give an award to the first one who can produce an easily collapsible stroller that faces both ways - and is affordable for all parents.""
Yes, there are some that can be used for both sides (that faces both ways).
They exist but don't know why are not so common. I asked my wife, she said that the ones she recalls that are 'both sides' had the problem that are very heavy to carry.
I don't think is a matter of affordability. I don't find any of them so much affordable by the way. I also think that perhaps is a matter of realizing on the importance of that or not, that's the importance of the article after all.

huh
When my son was born, we got a stroller that could face front or back and could also go into a complete reclining position. It worked pretty well except for the swivel wheels being in back for one of the configurations.
This son, now in engineering school, is absolutely brilliant, well-adjusted, likable, curious about the world, able to fix any computer problem, and not a fussy eater. Clearly the stroller was key in his development.
Oh, also he's very handsome. And tall and slim. I take no credit at all. It was the stroller.