Good question, one that has several heated opinions as well.
Some have sought out higher ranked MA players in the PI and gone to them for promotion. Some have promoted themselves. Some have gone to variously structured peer-boards for promotion, both inside and outside of established organizations. Some have simply promoted themselves.
At the time of Remy's death, there were a handful of high ranks in the PI, a couple of Punong Guro's and Senior Masters, and the 6 Datus, the majority of these last 3 groups being in the 5th-6th degree range. According to several accounts (including archived news from the old IMAF), the highest tested rank, at least in the US, was Hartmans back in 2000. One could make a reasonable assumption that the rest were time in or other types of promotions. Theres a ton of players out there though. (Theres blanks in my memories so please forgive any errors/omissions)
3 of the Datus are active in the US, and 1 active in Europe
Tim Hartman, 6th under Remy, 9th under the WMAA.
Kelly Worden, 6th under Remy, 10th?? under WMAC
Shishir Inocalla, 6th under Remy, ?? now?
Dieter Knuttel (Germany), 6th under Remy, 7th now
There are the 2 IMAF's
Jeff Delany's (5th under Remy, 10th? now)
Randy Schea and the other MOTT's (all 5ths under Remy, not sure of current ranks)
As well as MARPIO, IMAFP, and numerous independents.
The politics side is a mess, as reading a number of older threads here will show. Short summary:
Tim Hartman announced his departure from the IMAF and formation of the WMAA in late November 2000. Remy's retirement was announced at this same time. In mid 2001, Remy died, and shortly thereafter the IMAF split into 2 factions. Several individuals also went independent or formed their own organizations during this time. Numerous others became more active/visible. Very shortly after Remys death, his children formed their own organization as well. So, on the surface, it's a mess. But, not really.
Each organization has it's pluses and minuses. Try a few groups out, see who you 'gel' with, and enjoy the training. Check everyone out if you seek rank advancement, and go with who you feel most comfortable with. Most groups are pretty similar, though their focus and terminology may differ a bit depending on various things.
Note: My minds foggy, so I may have some things incorrect or in the wrong order. Corrections welcome.
Disclaimer: I'm a long time friend and student of Tim Hartman's, so some might see my opinion as somewhat biased. So, get a few more