I believe Bangladesh should be playing more Test nations 'A' teams, that they, especially against the likes of England, India. SA, and Australia, they'll be getting a competitive game that they will take a fair bit of confidence out of a victory against them and they will no doubt have to work hard for it. They need to learn the art of winning, currently they're plundering from one hammering to another. Once things begin to go against them it is unsurprising that they start thinking 'here we go again', they don't have any positive experiences of winning matches.
Their standard of first-class cricket is an obvious area of concern. Players that are managing good results in domestic cricket are still some way from being able to transfer that into Test cricket as the gap between the two formats is inevitably huge.
I don't think the argument of 'look how long it took NZ and SL to become competitive' necessarily works. Yes it does take a side some time to adjust to Test cricket, but those two nations are not a blueprint for how it should be done, the ICC need to be looking at ways to avoid countries having spend year after year getting slapped about before they begin to get competitive.
Tamim Iqbal, Shakib al Hasan, and maybe Mushfiqur Rahim are reasons for Bangladesh fans to be hopeful for the future. It is good to see the likes of Shakib playing County cricket, to help develop his game, and I would hope the other two are looking at options to enhance their first-class playing experience at a higher level than their own domestic tournament.
I would Bangladesh mixing with the big nations on an ODI level, but at Tests, imo, they should be looking at playing top nations 'A' teams.