It's similar to how encryption was viewed as too expensive a decade or two ago. Today, it is a necessity. Seeing how available bandwidth keeps growing to accommodate things like video, I hope traffic analysis defenses won't be as detrimental in the long run for most internet use.
Yes, for sure. As a defender, you have two main tools: dummy packets (bandwidth) and delaying packets (latency). Padding-only defenses will indirectly delay normal (non-padding) packets by filling the connection with padding. You want to explicitly block outgoing traffic and try to account for congestion to minimize wasted bandwidth.
This is tricky. We have hardly started dealing with traffic analysis issues in protocols. In general, we have spent the last decade+ getting encryption sort of right with amazing efforts like TLS 1.3 and WireGuard, etc. Expect another decade for traffic analysis.
Nope, "AI". The academic community working on one very active research area of traffic analysis, called website fingerprinting, made significant leaps with NNs over traditional ML in 2018: "Deep Fingerprinting: Undermining Website Fingerprinting Defenses with Deep Learning", by Sirinam et al., https://dl.acm.org/doi/pdf/10.1145/3243734.3243768 . Since then, the most powerful attacks here have used deep learning.
Broadly speaking, traffic analysis benefits a lot from work in computer vision: view a network trace as a one-dimensional picture. There are some fun visualizations here if you scroll down a bit: https://github.com/pylls/padding-machines-for-tor/tree/maste... . Every 1-pixel high line is a website visit, where each pixel corresponds to a packet (or cell in Tor) sent or received.
Yes, it's significant. Unfortunately, there are fundamental trade-offs here between protection and bandwidth and/or latency. Another aspect is energy: keeping a connection "alive" by regularly ensuring traffic on a connection does not help battery life. We have much to optimize here.
For what it's worth, as part of work on the effects of DNS on Tor's anonymity [1] we visited Alexa top-1M in April 2016, recording all DNS requests made by Tor Browser for each site. We found that 6.4% of primary domains (the sites on the Alexa list) were behind a Cloudflare IPv4-address. However, for 25.8% of all sites, at least one domain on the site used Cloudflare. That's a big chunk of the Internet.
It's similar to how encryption was viewed as too expensive a decade or two ago. Today, it is a necessity. Seeing how available bandwidth keeps growing to accommodate things like video, I hope traffic analysis defenses won't be as detrimental in the long run for most internet use.