Currently nether wart blocks are just for decoration. I think it makes perfect sense for it to act like Hay Bales and Iron blocks, which can be broken back down into their original materials. I honestly was surprised that this was not a thing yet.
You have much company, the irreversible crafting of both netherwart and nether quartz have been repeatedly questioned...
In favor of the current situation is the consistent behavior of nether products as none [quartz & wart being the only examples of which I am aware] can be freely changed between block and single form.
An argument has also been advanced that this works to increase the value or luxury status of the block forms…
This makes more sense with quartz [a non-renewable resource] as crafting any of the block variants permanently remove a 'critical' resource from play. [Oddly, the competition for this resource between teh N-quartz builders and the Redstoners rarely seems to be the basis of conflict; either real or as 'just cause' for a friendly 'war'. ]
Given that even quite small N-wart farms can continuously supply multiple brewing stands [blaze powder or some of the 'special ingredients' generally being the limiting factor], it is hard to see how this argument applys to N-wart.
That N-wart blocks are (barring their color – a criterion very much YMMV) entirely unimpressive as building materials (low blast resistance and no special properties, including having no slab, stair, or other alternate forms) and have no other uses further weakens this argument.
(N-wart blocks were also added after N-wart could be grown outside the nether, voiding any argument that this inconvertability was intended to enforce a transport bottleneck.)
The main advantage N-wart blocks hold is a (fairly) low hardness , making them the lowest hardness (ie fastest breaking), renewable blocks that drop themselves other than haybales (which are flamable). [Given a silk touch axe, melons are mechanically equivalent and easier to obtain.]
While either custom crafting recipes or villagers with custom trades offer easy ways to add a method of back-converting the blocks, I see only trivial effects (and those positive1) from adding the suggestion to vanilla.
1I would expect a (very) small decrease in lagginess if players store N-wart as blocks due to the nine-fold reduction in the number of chests needed for a given quantity.
Making the two forms freely interconvertable would also remove a possible (if rare) form of griefing.
[I have been unable to think of a negative effect of this change; the only use I've actually found for the block is as a marker in sorting systems (replacing an item in a frame), and the plant form (while not a garbage item) is somthing of which I rapidly have a surplus.]
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.