Interesting, I never thought of the coming next week trailers as spoilers for anything since they are made to intentionally misdirect and just get people to WANT to watch the next episode (not that GoT needs extra hype or a reason to tune in). Some of my favorite little things about TV trailers, and this might be a little inside baseball (futbol for you non Yanks) but a lot of showrunners put their trailers together to actually kind of troll the audience a little bit anyway. Most famously, if you've ever watched a "Next Episode" trailer for Mad Men, it would literally just be shots of people opening and closing doors and hanging up phones, so you literally have no clue what is coming next except... people will be opening and closing doors or answering a phone.
I expect the remaining episode trailers for GoT to be something like this: DRAGONS! WHITE WALKERS! MORTAL PERIL! Someone getting knocked down but who is it? Fire! Ice! Characters looking scared or angry or brooding. 30 seconds is not really enough time to spoil much of anything, unless they are revealing some unknown character appearing, which I don't think they'd be dumb enough to do.
Movie trailers however, can be different. I have seen 2 minute movie trailers that not only essentially spoil a movie but have all the best jokes and action shots already in them. That to me seems foolish, but again, it's a matter of showing people something that gets them to want to go watch it. Game of Thrones is in the unique IP situation of people tuning in no matter what. It could essentially have no PR at all and would still draw massive ratings.
To each their own.
Take care all.