Now concerning the next update, do not worry, it won't take more than 1 update (max 2, depends on how much time I can spend on the game this month).
They won't be on the yacht. It will be new location, that's part of the reason I want to do it, we've been on the yacht for a while now, it's time for temporary change of scenery.
About Susan / Rachel content, it will come, I want to do it too, I just need time. I spend almost all my free time on the game to bring as much new content as possible every update.
So far the game is very detailed with lots of content and so progression towards certain themes or characters may seem to be slow.
Looking at the npc progression overview at current version (0.4.3 100%) :
Rachel : Corruption 0/3, Exhibition 1/3, no Traits revealed (1/9)
Susan : Corruption 0/3, Exhibition 0/3, Traits : unknown, unknown, bondage (1/9)
Linda : Corruption 0/3, Exhibition 1/3, Traits : unknown, lesbian, unknown (2/9)
Amy : Corruption 0/3, Exhibition 0/3, no Traits revealed (0/9)
Emily : Corruption 1/3, Exhibition 1/3, Traits : unknown, anal, public (4/9)
Chloe : Corruption 1/3, Exhibition 1/3, Traits : impact, humilation, voyeurism (5/9)
Overall :
Corruption : 2/18
Exhibition : 4/18
Traits : 7/18
-> total : 11/54 = 20%
Some characters like Rachel already had a lot of content so revealing her traits or increasing corruption may be well prepared and probably only require a small content update, so I guess current content is probably around 20-30% of the full game if development continues with the same degree of details. Since some of the costly features like the nice spanking marks system are now implemented, character progression probably may speed up a little bit in the next updates.