Several improvements can be made to make OPORCON competitive to commercial products. All of these will change OPORCON controls, as iButtons are proven technology, used commercially in numerous factories for time attendance, metros as e-tickets etc.
Better timing: by using an RTC in the control, much better accuracy can be achieved. Easiest way is to add 1-wire RTC like DS2417 because OPORCON already has support for 1-wire in it's program. Price of such system will put the price up a few euros, and give accuracy better than +-4 seconds per day (in the worst case without using a timing enhancement system already programmed in OPORCON).
Update: David Deane and Bjorn Dinse changed the oscillator to get better timing. Achieved accuracy is now +-1 second per day.
piezo speaker can add audio signaling for the price of few euros.
Update: David Deane added a buzzer.
Programability: current OPORCON system needs per control chip pre-programming, because of timing enhancement system which is dependent on element on the control board. 16F628 used in this system can be programmed when it's on board, by using In-circuit Serial Programming. Change to the schematic can make re-programming of controls easy. This won't put price up, it's a simple rearrangement of elements and one connector.
emulator box - a box which can read OPORCON iButtons and produce output equal to SportIdent's or Emit's, so existing software can use OPORCON.
flat card - as iButton uses only 2 wires, a flat card similar to EMIT can be made. Card receptor should have distinctive shape, and two separated lines for connection - maybe one on each side? This way backup can be made in EMIT fashion.