I'm not sure if anyone has suggested this yet. (I couldn't find any suggestions similar).
But I think it would be amazingly cool if a /write commands could be added.
A predetermined set of characters would be able to be cuboided using the /write command.
e.g. /write <block type> <message> or you could just, you know, manually select the block.

It would also be good if, maybe at a later date, a text size could be added. The default or first coded in would around 5 blocks high is think (based on other write-style commands I have seen) as 5 blocks is enough to accurately portray all of the letters. Perhaps, in relation to the variable sizing option, you could choose in multiples of 5.
e.g. /write <#scale> <message>
If this could be coded I would be very happy.
Thanks.
MoleManMike.