Unfortunately that's not the fault of the FFXIV but rather SE as a company. FFXIV 1.0 was a failure and though they had great succes with 2.0 there were still many times in which YoshiP would cite "not enough resources' as a reason why they couldn't provide something which is -usually- developer talk for not enough funding. There was even an interview where he spoke about needing to hire on more battle content developers because they were so short staffed. Now, one would think they should just be able to take from with SE itself, but SE is, unfortunately, notorious for taking people off of one succesful project and dumping them onto another project they hope to bring succes to (Rumor speculation in this case is FFXV but there has been NO OFFICIAL confirmation of staff or funds from FFXIV being reallocated to FFXV)
It's frustrating, because through various sources, things you can read in interviews with YoshiP and even googling for information involving SEs earnings and the like, it should be clear that this game does not need a cash shop, yet the proceducer himself up and said when it was created that it was being done so to fund other projects they wanted to do for FFXIV, with the EU servers being the first ones names. Yes, SE as a company should be providing the FFXIV staff with the funding to do this, but, for whatever reason, shielded behind doors we can not see through and conversations we know nothing of, it's clear that this is not happening but why it's not happening is what we don't know.
The Cash Shop is, whether one likes or not, a feature that YoshiP felt the game needed for him to provide certain aspects to community that they wanted. Yes, it sucks but that is the reality of the situation.
Thankfully, at Fanfest 2016 in Vegas, it was said that Stormblood has triple the budget of Heavensward (Source: Me, I was there), so hopefully that means the unqiue cash shop only items we've been seeing (such as Selpnir and the Mog mount, I don't count regional exlusives as unique cash shop content because those aren't done by complete choice on the FFXIV Developers side, those are part of a contract negoation to allow the game to run in closed markets), will start to die down and it'll go back to mostly one off items and seasonal items of days past.
Two quick things I want to touch on here, since my reply above does cover some of this but:
Inventory Expansion could not be done at Heavensward because of the PS3. It's been said many many times the PS3 was a huge huge factor in expanding the inventories. Stormblood will be dropping the PS3 which will allow the FFXIV team to upgrade their infastructure as needed in order to expand inventories.
I'm guessing, and apologies if I am wrong, that the mount you are talking about is the Moogle Mount. Now, I do not disagree that the price is OUTRAGEOUS. However, it has been stated that the reasons for the price tag is because it is a flying, two seater mount that is account wide.