Steem it inc have said that this is reletavely low amount of work to achieve.

At Hive account@threespeak, we have been discussing light accounts with steem it inc for almost 10 months now, since we see it is critical for app development , scaling and onboarding and for investing in smts

Light accounts should:

• not be able to comment, upvote, vote, contribute to inflation Mechanisms, power up, or interact in any way with the chain apart from the following:
• Move steem
• Move smts
• One private key
• free Wallet / account creation
• either app or user covers small transaction fee if required
• They do not need a customisable name initially as the urgency of them being available cannot be underestimated and we would like to cut dev time down as much as possible. Custom name could be added later on

LA’s would enable threespeak and it’s users to:

• tip any one any where any time, in steem or Content creator smt even if they don’t have a block chain account

• Allow anyone to purchase an smt even if they don’t have a steem account (particularly good for projects doing icos or raises)

• Allow none steem users to easily acquire steem in order to purchase in app services / products / experiences

• allow anyone to make auto, passive micro payments to consume content (ie 0.001 steem per view or per minute)

• incubate and retain users before upgrading to full steem account

• plus Miriad other factors that u might need to use steem without having a full steem account

It is our understanding that light accounts can be implemented fairly easily in the next hard fork. We are urging a campaign to try to achieve it. We cannot understate how important it is for the scaling of apps here on steem