I don't see how octillery is a cheap shaymin, it's not in theory and in play they are 2 completely different cards regardless of if they offer a "similar sort of effect". Granted it could be good of it's own ability uncomperable to anything else it's just a matter of developing a niche deck engine that works for it.
Sometimes I wonder if this is a competitive thread, to me being competitive is not asking if something could or can be better then the existing, it's what it offer's and what can be done to get it to that level, if it doesn't hit that level drop it and carry on.
I think you missed the point. Pokemon TCG is full of cards that have very similar effects but have a clause altered to make it slightly different in practice. Octillery and Shaymin are an example of this - one is a "When you play", while the other is a "Once during your turn". Despite the difference, both strive to add a particular something to a deck - draw power. Now, as we all know, Shaymin has been an extremely powerful card since its release... so what does this mean for Octillery of a similar effect?
Immediately a competitive player will analyse and evaluate Octillery, to determine if it could be used as a budget replacement or even a total replacement of Shaymin-EX in some situations. When you consider that Octillery could provide you a reliable stream of draw nearly par to Shaymin-EX
every turn while avoiding popular Shaymin counters including Silent Lab, there is
definitely potential use as a budget replacement card, especially for those people that cannot afford three Shaymin to stick in a deck. If I can achieve a similar draw to that if I used Shaymin, but for cheaper, than would that not be a "cheap Shaymin"?
Now, I'm not saying you can replace Shaymin-EX with Octillery and call it a day. Shaymin-EX has the primary niches of providing early-game draw, relief from a dead hand and potential to combo to obtain all the techs needed for a play. Replacing all Shaymin will mean you lose these niches that are highly advantageous in a competitive battle.
However, I could replace two of my three Shaymin-EX with an Octillery line, and can use a single copy of Shaymin as backup. I will be able to fill multiple niches in this way at a
much lower cost while keeping similar draw power. If I really am low on money, I could swap my last Shaymin-EX copy with a Jirachi-EX, which provides similar niches,
especially when used in combination with Octillery.
In regards to the thread, keep in mind that the OP was asking for community opinions on the following topic: "Will the price of Shaymin-EX be affected by the release of Octillery Breakthrough?", which inevitably lead to the discussion of "Octillery or Shaymin-EX?". Also keep in mind that even the best of best will ask questions such as "Octillery or Shaymin-EX?", and discuss said questions with their peer group. This a healthy mindset to be in, as you can both sharpen your theorymon and discover new uses of even the most basic cards (see Hugh in Wailord-EX). A community of casual to competitive players have gathered in this thread to discuss the viability of Octillery, which is a great example of a competitive community working at its best.