So I was thinking about this some, and before I get into solutions I want to make sure I understand the problem. If I am reading you correctly there are actually three problems here:
1) People DCing in the middle of scenes
2) People not sticking around to RP or committing traditional RP avoidance.
3) Slow posing speeds.
If this is true, then below are my thoughts and suggestions. If this is false just go ahead and ignore anything after this point.
1) People DCing. I really don't have a good answer for this one. I am lucky in that I have a client on my smart phone so I could hop on and tell someone "Hey I got disconnected an my internet isn't coming back up. Can we pause this or just bring it to a quick end?" If I have cell service and battery. Some people don't have this luxury. Any code changes that would limit RPXP gain penalizes those who have legitimate reasons for DCing. If there is someone who is abusing the good graces of the community by doing this all the time, it should be handled on a case by case basis by Policy and potentially nerf their XP pool. Don't light the whole barrel of apples on fire because of one or two bad ones.
2) Ok this one is annoying and just has to stop, with a couple of exceptions. People pass through the Crossroads all the time. If I had to stop and pose every time I entered into the crossroads, and there was someone else there, I would just avoid the crossroads. If however you are in the Queen's having a drink and someone you don't like walks in, don't just log out, a quick little emote should be sufficient. I will admit there are characters in this game that my characters just wont associate with. Walking out should just be fine with an IC reason. Blatantly avoiding RP through OOC means is not cool. I don't, however, know how to penalize someone who is a habitual abuser. Seems to me that this should be referred to Policy.
3) This one I take the most issue with, and here is why: I type slow. I type even slower on my phone. So during the work day (and there are several of us like Geras said that log in from work on our breaks and such) are going to be slower by nature. Second, our posing style of ParaRP builds in huge time delays. Frankly if you wanted me to pose big poses, you are looking at a good 10 minute turn around on my computer and upwards of 20 on my phone. THAT IS TO THINK UP AND TYPE THE POSE. That doesn't take into account reading the other person's emote.
So, what do we do about this? Well there are three things I can think of off the top of my head:
1) Limit pose length - Nonstarter since we are known for our ParaRP
2) Eliminate MultiPlaying, allowing only one character logged in at a time focuses the attention at the task at hand
3) As a community set some sort of posing speed/length standard, and if you can't match that, don't log in. That would probably thin me out completely or
down to a couple hours a week in the evenings.
TLDR: This is more a community problem than a code problem. Commitment to a scene must be an important community value, tempered with the fact that there will always be unforeseen issues. Posting speed will greatly reduce the number of people able to RP in the short run, but maybe it will attract more people in the long run. I don't know. If you want to see short term gains the best answer is to force people to not MultiRP so their only RP focus is on the TI character they are logged into.
(For those who are curious this took me half an hour to write and proof.)