Always risky to play on index inclusions and departures. If one looks into the history of these frequently hyped up events than all one often sees is some SP volatility around the event (probably more from the hype than from the index transactions), but it is quite rare that the SP moves long term due to the index event.
If OCA will be included into the NZX 50, than all which happens is that the NZX All Ord Index funds move their holdings into the NZX 50 index funds. No big deal.
Obviously - OCA might go up due to other reasons - like great PE in combination with lots of growth and favourable population demographics. Recent gummit decision might help as well (no CGT gives our bulls one reason less to down ramp) - and obviously ... it is not just me who sees them as undervalued (check analyst recommendations:
https://www.marketscreener.com/OCEAN...010/consensus/).
Discl: happy holder, but don't expect fireworks from any index inclusion.