So LHR-HKG is 90 tier points one way and LHR-SIN is 100 in premium economy. Let's say you do one each monthly; that's 380 tier points a month or 4560 a year before you add in the South East Asia short hops in Y which is almost enough to earn GGL and a Concorde room card if you go with BA's executive club (you need 5000).

When I joined BAEC, upgrades using Avios (UuA) was relatively easy to do for not too many points. These days it costs more but once you hit Gold (after 1500 tier points which would be about four months) you can earn enough Avios for a one-way upgrade to biz on BA every third flight or so.

The one flaw will be travel from SIN to other places in Asia (except HKG) since SQ is Str Alliance and you won't earn points on those flights. Using Cathay from HKG would be fine for earning Avios and tier points.

As others have said, comp upgrades to biz are rare (though not unheard of and the sweet spot is buying WT+, especially once you are Gold). But if you can use Avios every third leg, that's not so terrible.