For someone like me who's 50+, doesn't race, and was focusing on long term comfort for multiple hours in the saddle, I think they work work better than anything else out there at the moment, especially that you can go with 30+mm tires. I have multiple bikes for different purposes though.
When the need arises for flat out stiffness and speed, there's other options. I test rode Trek's Emonda series and was pretty impressed. I would prefer that over the Tarmac any day.
If I could only choose one for most of the riding I do, I would go Roubaix in a second, for the way "I" ride, but that's not for everyone.
I do think a few other manufacturers are looking at some options, but probably keeping an eye on sales to see how these FS equipped bikes are doing. Its only been out a year. I can't speak to long term maintenance yet either for that reason.