I hope MPTCP would be more popular

Many src-dst connections but as a single logical connection. There's no way any middlebox could easy capture full data even metadata.

http2/QUIC can do something similar with frames (and hopefully multipath)

Don't place your whole stream inside a single src-dst IP connection. Demux them into many paths over the Internet. We need more variety of "traffic shapes" to combat Internet surveillance.

I'd argue it's even more effective than encryption. Split your activity and mix them, monitor traffic over a single transport is useless.