You get "more stuff to see" on Mobile and Console because those are ports of known content. What secrets are there to keep there that are not on the wiki, etc. - outside of "hey look it's here" or "here is some tweak/difference because of the different way X platform works"? We can tell you "it's 1.3.4" and everyone knows what that means - so that is by definition a VERY different scenario than a major NEW update like 1.4. That can be good and bad....
In regards to your particular complaint - we have shown a TON of spoilers over the months (see: Spoiler Compendium thread) and in the E3 trailer. There is so much known about 1.4 already. However, we always have kept some things secret - and we will continue to do so. Just because "you only got to see a broom mount" in the SOTG, that does not mean that the development team is sitting around and that is all they got done... nor that "1.4 is done and Re-Logic is secretly scheming in the villain cave to sit on this". Some fun speculation there, but I'm afraid it is quite far from the truth.
The dev team is working every single day on 1.4 to get it to where we want it, with all the things we want included and working in the ways that we want them to work. When that process finishes, then you will see things like exact release dates and the launch. We have never held Terraria to artificial deadlines so that we can rush things out, and we are not going to start doing that with 1.4.
As for the other platforms, it is great that they are catching up - how does that harm anyone to see Console and Mobile and Switch rolling out 1.3.X updates and the like? That said, it would seem like a pretty big stretch to assume they are going to somehow have 1.4 already - so I think you may have conjured up a conspiracy theory there.
As for the other questions....
- The SOTG comes about the same time each month... it is not "coming later and later" each month. The exact timing has to do with how dates fall and what news might be available and when, etc.
- Console 1.3.4 will only be through 1.3.4 and will not have 1.3.5 content yet. So, anything that came in 1.3.5 will not be here... which should only be like 20-30 items
- As soon as Re-Logic gets a final test build on Switch 1.3.1, we will check it out - PW is still working on some touch implementations before then, however.
- My understanding/take on Split Screen is that it is still up in the air a bit - it does exist now in test versions, but it needs to meet certain minimum performance standards before it can be called "ready"
- By this, we mean things like severe FPS drops... or control input delay, etc. Things that would materially impact play for either player.
- If it isn't "up to par" yet, then I can see it being pushed to post-1.3.1 and then PW doing continued deep-dive work on SS to get it where it needs to be.
- Mobile development "slowed" a bit in October to allow the DR folks to take a much-needed and well-earned breather.
- 1.3.0.7.6 is needed because of a handful of issues that cropped up with 1.3.0.7.5 - we cannot just leave those blurry NPCs out there, for one.
- Controller+Customization is then at long last the front of the line for development work - I know the team has a TON of ideas there and cannot wait to get started.
In the end, everyone really is giving their all across all fronts to get everyone what they want to see. Sometimes that may not be exactly when you want to see it, but we have to stick true to the processes and standards that have brought us this far. Shoving out substandard work has never been our way. All we can say is to hang in there and trust that tons of good stuff is coming - on top of the great things that have already arrived for Terraria thus far in 2019!