We handle multiple individuals within a family exactly as other posters have suggested, by creating a "Household" bundle that we limit to 6 members - and I like this approach. It makes the principal member responsible for a membership package and payment, whilst allowing all bundle members to receive communications.
Having said that it does count against our overall contacts database allowance which is clearly a downside for our organisation cost wise.
As Chief_Apricot has said this is really an issue for WA in their pricing and structure of levels, rather than an additonal feature request.
Could you simply review the database limits for each level of WA service - perhaps 500 / 1000 level change between group & community rather than the 250 / 500.
You could also make a simple offer such as, "Every 'bundle' membership can have one secondary member at no cost to your WA limit"
A more complex alternative idea: perhaps WA could consider the possibility of effectively discounting "bundle members" to some extent. You could do this by keeping your existing levels limits the same but treating bundle members as being less "valuable" or a fraction (in terms of how they count against our allowance) of an ordinary entry.
I like the technical solution as it stands, so these are just some of my thoughts on how to get to the same end result at less cost for us WA users.