Creating something new is like asking for the impossible. I'd assume that everything iSRO has come directly from kSRO and has taken forever for updates so you have to keep things REALLY simple or use some existing stuff.
The only guild activities I see are Trading Runs (TR), Thieving (T), Unique Kills (UK), Guild Wars (GW), and Union Wars (UW) but TR's aren't profitable for the time and risk; Thieving also isn't worthwhile; UK's are impossible to get to yourself; GWs are hard to set up, UW are even more difficult to set up.
Improving Trade Runs:
+++This is supposed to be the center point of SRO but it's not worthwhile. Impoving this alone will help improve everything else as GOLD SHOULD BE one of the motivations. It would increase trades, increase guild trades, increase union trades, increase thieving, increase rivalries, etc etc.
-Increase profits
-Keep a mercenary alive from one town to another for GP rewards?
-Leaders can summon more than one transport?
-Guild trade animal? + NPC Rider for GP?
-Union trade animal?
Improving Unique Kills:
-More spawns
-Spawn Lord Tsarkon
-Spawn Saytan
Improving Thiefing:
-See Trading Runs
Improving Guild Wars:
-Average the levels and give way more EXP / SP, at least half the EXP loss when you die. At the current rate it's 20 kills for 1 death!
Improving Union Wars:
-See Guild Wars