The seemingly unstoppable rise of cryptocurrencies continued this week, extending a big rally that stretches back to early October. Quite a few altcoins were swept up in the surge as major coins led the way.

Among the risers was Cardano (ADA -3.14%), with a nearly 18% increase according to data compiled by S&P Global Market Intelligence. Even more impressive was Polygon's (POLY) 26% pop. BNB (BNB -2.40%) and XRP (XRP -1.49%) didn't quite hit those highs but still managed decent gains of over 10% and nearly 9%, respectively. Continued good news was the flame that kept the rally alight.

Crypto spot ETFs are on the way, hopefully

In this market, it's often one of the giants that leads the little guys along. This partially explains the rise of altcoins particularly at the end of the week.

You see, much of the bullishness with cryptocurrencies at the moment is due to investor excitement about spot crypto exchange-traded funds (ETFs). If and when these receive regulatory approval as valid, investible securities, demand for their component coins and tokens should rise suddenly and dramatically.

On Thursday, large and influential financial services company BlackRock filed to list a spot Ethereum ETF on the Nasdaq. Does that sound familiar? It should, as the company previously moved the market with its attempt to bring a spot Bitcoin ETF to life.

While there is currently a clutch of crypto ETFs available for investment these days, none invest in coins and tokens directly. The spot ETFs would function this way, and as such they would be more closely representative of actual coin and token prices than the currently available offerings. They'd also be quicker to buy, and easier to hold, than direct crypto investments.

Recently the Securities and Exchange Commission (SEC), famously resistant to cryptocurrencies, suffered a legal setback in its fight against such assets.

This summer a District of Columbia appeals court ruled that the regulator was wrong to turn down Grayscale Investment's application to convert its Grayscale Bitcoin Trust into a -- you guessed it -- spot Bitcoin ETF. The SEC subsequently decided not to appeal. Compounding that, the Commission this week reportedly launched fresh discussions with Grayscale about the process.

This understandably boosted optimism in the crypto community, and it was only compounded by BlackRock throwing its hat in the ring for that spot Ethereum ETF.

Imagining a spot altcoin ETF (or several)

True, no one is yet concocting a spot Cardano or Polygon ETF (at least as far as we the public are aware). Yet if and when such financial instruments hit the market, at least a few of the prominent altcoins will form the core of such instruments. We can even imagine a general altcoin ETF or several prowling the market. Why not? There are obviously plenty of bulls who would consider plowing money into them.