I think there needs to be a tier of countries who are nearly ready for test level cricket (including Bangladesh) and do a promotion and relegation system based on their performance. So you would have countries like Kenya, Bangladesh, Zimbabwe, Scotland, Ireland and The Netherlands battling it out in test conditions for two spots.
Theoretically even the top tier teams could be dropped down to this level if they have a very long streak of poor performance and the lower tier teams could become full test nations with large amounts of good performances.
The problem comes when there is a huge gap between the skill levels of the top and bottom tier teams, but if there is enough cricket played the lower teams can build up good squads and you could see an expanded 'top' tier of teams who are all competitive. Or alternately the top tier could shrink so that there is huge competition in both levels.
As for Bangladesh specifically, the thrashings don't help them, they might be better off sticking to ODIs, but they need to play a lot of test matches to become a good side, one day they might make it if they keep at it.