But why though? It seems like the housing update (in how many weeks?) will render that a moot point as you'll be able to put in herbs and crops both, and presumably have greater license in decorating, not to mention the house will be in your own head.
Also, from a game mechanics & economy the new houses will serve as a significant "credits" sink. A maxed out house will likely take millions of imagination.
E.g. 32 crop garden plots, 32 herb plots, 5 floors, 64+ slot cabinet, 6 tree plots, animal pen, etc. Every time you increase size the cost will multiply, plus I suspect there will be an upcharge based on features mix you have, ie adding 6 more garden plots will cost 100, but 6 herb plots would cost 120 (since you now have both)
Then there would be no houses left for new players.
A better solution: You can only own up to a certain number of garden plots and you can only visit each house a certain amount of times each day. (example: You can only have up to 30 garden plots and can only visit your houses six times each day.)