IMO the only "fail" part of the DLC was charging for stuff that was already on the disc (MK1 costumes).
That's true, but I strongly think that, they had to do it in order to justify the pre-orders. Assuming that if they didn't do that, then the customers who pre-ordered the games probably wouldn't pre-order again because then they would think "why even pre-order if you are going to get the costumes anyways later on?". Therefore in order to assure that the pre-orderers are happy they charged all costumes for a rather small fee.
7 costumes for 5$, which were pre-order exclusives, think about it, sometimes pre-order exclusives aren't going to be released at all, therefore the charging was
somehow reasonable. But of course the costumes were already content on the disc and therefore they charged people for something they already should have access from the being with. It's clear, that this had upset many people and I really think that the classic skins on the compatibility pack were a kind of retribution from NRS's side to pour oil on troubled water.
If you see it this way then it's understandable why they chose the ninja costumes additionally to the presumption that the chosen classic skins in the compatibility packs were used as a promotional material.
Of course it's impossible to appease and satisfy every person, because nothing is so hard as man's ingratitude. But leaving this aside I am very happy for the outcome of the classics (for now, I am still hoping for more though. Nevertheless I am very thankful for every classic costume they give us, be it free or not!)
Other than that it's fine so far, just be patient

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That's a word! If the sales rates are increasing then the probability for more DLC will also rise. I won't be saying that this is a linear dependency because it's hard or even impossible to quantify man's motivation but looking at other things will tell you that money was always a motor for motivation
