Like pretty much everything these days, trade shows could use a bit of re-inventing. I don't think the online "shows" are a threat to the in person shows. The formula just isn't there. But I think work load and tight budgets are competition.
Shows/conferences need to look for more activities that can only happen live and in person and are more valuable than the cost of plane, motel and a weeks engineering time.
I hear a lot about the aging of the engineering work force, and I think there's merit in that train of thought. But there are also plenty of younger engineers and they operate differently. Their sense of time is different. I can remember a time when contracts went back and forth by snail mail, parts orders took weeks to arrive and prototypes were built by hand.
Now "paperwork" goes back and forth instantly. An engineer can go from CAD file to finished prototype in just a few days. Everything is compressed for these folks and that needs to be accounted for.
I looked at several conferences this year and the price tag was significant when including a continental flight. At least for US travelers elevated travel costs may have crossed the breaking point? It definitely has for small businesses like the one I currently work for.
Isn't that the case for a lot of European tech shows? I remember when CEBIT used to be an important show.... but the last few years, it's been a tech graveyard. I don't feel like shows in the U.S. or Asia are getting any less busy though, so maybe Europe is the problem.