i think this "gate" will be open when the house of wolves DLC is released cause as someone else said they have guards protecting the shit out of tat place... so maybe the Queen is behind it and you have to visit her as you do Eris Morn in the center of the tower. But contradicting this idea is the fact that it looks like there is an entire city behind there (as you can see if you go to the entrance of the speaker area). Another idea is it s the rest of the factions who weren't allowed a seat in the council of the tower so they act as vendors instead of reps (or they could act as reps). And as someone said they hopefully have plans for the next 5-10 years including the next destiny game entirely (which we have Jupiter, mercury, and Saturn to expect from). We can keep guessing as to whats behind there and be off by 1,000,000 miles or we can focus on what we have and whats to come (house of wolves). I hope this helps with your question if not just ignore it.